DE3943488C2 - Process for reducing or eliminating free formaldehyde with carbamates, which are generated on the substrate in the critical phase when formaldehyde is released - Google Patents

Description

For use in plywood and particle board production with aminoplast adhesives, carbamates are used as formaldehyde scavengers proposed using binary reaction mixtures be prepared so that at the same time Carbamate bil the, as soon as formaldehyde when curing z. B. urea Formaldehyde copolymer glue is released. Such one binary reaction mixture consists of solid urea and one Component which is the carrier of acidic OH groups. This binary The reaction system can additionally contain a catalyst.

Model reactions show that acidic OH groups, in particular semi-acetal OH groups, in contrast to ge usual alcoholic OH groups, in molten urea Add isocyanic acid very quickly and completely, whereby Carba mat groups form and all subsequent reactions with the first Reaction steps are determined that are completely different fen than with ordinary polyalcohols such. B. sorbitol.

With the help of a binary matched by a catalyst Reaction mixture can the production of carbamate groups can be controlled that these at the same time and in the correct Quantity with the release of formaldehyde when hardening from uses the relevant aminoplast adhesive. This temporal Ab adjustment of carbamate production with formaldehyde development allows the extensive elimination of unwanted free Formaldehyde in the finished products without the known Disadvantages of urea accepted as a formaldehyde scavenger must be like the results of the examples in the patent registration dated May 4, 1988 with the official file number Document P 38 15 204.5.  

In the series of tests, the desired optimal are compared side equivalent ratios - acidic OH groups / solid Urea and solid urea / ammonium chloride - empirically set so that the formation of carbamate coincides with the Release of formaldehyde during curing from the adhesive it is true that at the end a tolerable residual content up to towards the complete elimination of free formaldehyde is achieved.

In the patent application dated May 4, 1988 under number P 38 15 204.5 and with the title - Process of manufacture of composite materials with reduced formaldehyde emissions - it is said in the claims that the "form aldehyde scavenger in prilled form "on the material to be glued applied or mixed before gluing or the Formaldehyde resin is added.

This formaldehyde scavenger, which is labeled in this way, also becomes other known formaldehyde scavengers such as melamine (e), Dicyandiamide, thiourea, dibutylthiourea, ammonium carbonate, polyacrylic acid amides, guanidine, carbamates with free Amide functions, phenols, resorcinol or diphenylmethane diiso cyanate and especially urea.

With the present invention, the above-mentioned "shape aldehyde scavenger in prilled form "degraded to chemical, which belongs to a binary reaction system, with the help of it it succeeds in curing the aminoplast adhesive in the hot press to catch escaping formaldehyde.

Urea-formaldehyde copolymer and those with this type of Adhesive related chemistry is described by A. Pizzi (WOOD ADHESIVES, Chemistry and Technology, edited by A. Pizzi, MARCEL DEKKER, Inc., New York and Basel 1983; in it A. Pizzi: Aminoresin Wood Adhesives, 59-104). The following from citations and references from this source each listed after "A Pizzi, S.....:".  

When curing the glued lignocellulosic substrates On the one hand, ether bridges form, especially between the cellulosic part of the lignocellulosic substrate and the Urea-formaldehyde copolymer, releasing water becomes; on the other hand, crosslinking of urea formaldehyde takes place hyd copolymer (A. Pizzi, p. 71: R. Steele and L. E. Giddens, Ind. Eng. Chem. 48: 110 (1956)) and also formation of cyclic Urons (A. Pizzi, p. 64: H. Kadowaki, Bull. Chem. Soc. Jap. 11: 248 (1936)), whereby water and formaldehyde are split off, which indicates the substitution of methylol groups by such Methylol groups is due.

The formaldehyde that is inevitably released during curing is allowed in the product according to the German E1 emission standard 10 mg form Do not exceed aldehyde per 100 g chipboard dry.

This standard can only be met if urea form aldehyde copolymer is used as an adhesive, in whose manufacture the molar ratio of formaldehyde: urea 1.2: 1 or better to be on the safe side <1.1: 1 has been pushed down, but so too prescribed standard for bending strength and transverse tension strength of the products can only be maintained if at a molar ratio of formaldehyde: urine during the manufacture of the adhesive substance ≧ 1.2 is observed; quite apart from the norm for 24-hour swelling of the products in cold water can only be met with a molar ratio of formaldehyde hyd: urea ≧ 1.2 or probably ≧ 1.3 (George E. Myers, "How mole ratio of UF resin affects formaldehyde emis and other properties: A literature critique ", For. Prod. J. 34 (5), 35-41 (1984); Chem. Abstr. 101: 40029b).

In practice, the procedure is often that of production of chipboard only the top layer chips with unreinforced urea-formaldehyde copolymer can be impregnated, however the middle layer chips with melamine resin reinforced urea Formaldehyde copolymer can be covered.  

With formaldehyde scavengers, the free formaldehyde content in the products can also be reduced without impairing the other properties of the products prescribed by standards. Urea has also been described as a formaldehyde scavenger (Edmone Roffael and Lutz Mehlhorn, process for reducing the release of formaldehyde from chipboard, patent specification 28 29 021, Int. Cl. ² : B 29 J 5/00, filing date: July 1, 1978; Hans Diem, Christian Dudeck and Dieter Merkel, methods for reducing the formaldehyde evolution from aminoplast foams, OS 29 17 064 Ci Int ^3: C 08 J 9/30, date of filing: 04.27.79; Edmone Roffael and Hans-Albrecht May, methods for.. Reduction of the formaldehyde release of chipboard and fiberboard veneered with finishing layers, patent specification DE 33 44 239 C2, Int. Cl. ⁴ : B 32 B 21/02, filing date: 07.12.83).

Urea is an effective formaldehyde scavenger. With form aldehyde forms methylol urea, the two amide functions Nene in urea are more reactive to formaldehyde than the amide function in the methylol urea, therefore the urine first Fabric preferably coated on one side with formaldehyde.

Methylol urea condenses more easily with urea than dime thylolurea, water being released and preferred Methylene diurea forms. Methylene diurea is like the higher molecular weight methylene urea-formaldehyde copolymers sensitive to hydrolysis in a weakly acidic environment, whereby formaldehyde hyd is released when the methylenediamide grouping dissolves. After the urea is consumed, the hydro lysed formaldehyde released very difficult from the higher intercepted amides. These are higher amides reasonably useless because it doesn't add to the adhesive force wear, because only methylol groups are able to do that with the hydroxyl groups, especially in the cellulose part of lignocellulosic substrate can form ether bridges (cf. A. Pizzi, p. 68). This wrong development can go as far as that the paradoxical situation arises, that when  more and more urea to the precondensate more and more formaldehyde is always formed by hydrolysis of methylene diamides too little urea is available to intercept (A. Pizzi, P. 83: P. R. Steiner, For. Prod. J. 23 (12): 32 (1973)). The the resulting resin then has a low viscosity and smells strongly of formaldehyde.

Urea, dissolved in the urea-formaldehyde copolymer, ent folds a pronounced depolymerizing effect, which the Her position of low urea-formaldehyde copolymer molar ratio of formaldehyde: urea difficult. In addition, such so-called E1 glues because of the high Levels of useless higher-membered unsubstituted amides are slow to react and accordingly only with aggres Allow hardeners such as formic acid to harden.

Urea as a formaldehyde scavenger, used as an aqueous solution, only makes sense if the content of free formaldehyde in the cured finished products should be lowered.

The present invention takes a different approach. Urea is not considered a formaldehyde scavenger, but rather Chemical used in the heat isocyanic acid and ammo niak supplies.

In general, the implementation of urea with alcohol bring about the dissociation of urea to ammonia and iso cyanoic acid (HOUBEN-WEYL, Methods of Organic Chemistry, Volume E4, carbonic acid derivatives, p. 177, Georg Thieme Verlag Stuttgart. New York 1983; T.L. Davis and S.C. Lane, Org. Synth. Coll. Vol. I, 140 (1941)).

The lower carbamic acid esters, which are also urethanes or Carbamates can be called technical in this way (P. Adams and F.A. Baron, Chem. Rev. 65, 567 (1965); Ullmann, 4th ed., Vol. 9, p. 115 (1975)).  

Technical processes for the production of carbamates from alcohols and polyalcohols, which are based on the fact that isocyanic acid is released from the urea when heated and is added to alcoholic OH groups are known; likewise the use of catalysts (Toni Dockner and Harro Petersen, process for the production of carbamates, OS 24 59 765, Int. Cl. ² : C 07 C 125/04, filing date: 18.12.74; Harro Petersen, Subraya Panemangalore and Manfred Eichert, mixtures of pentaerythritol carbamates with polyalkylene glycol ether carbamates and with alkyl alkylene glycol carbamates and process for their preparation, OS 26 20 010, Int. Cl. ² : C 07 C 125/04, filing date: 06.05.76). These processes for the preparation of carbamates are of no importance for the present invention because the reactions described therein usually take several hours. A long reaction time is also required for the production of cellulose carbamates (Herbert Griesser, Thomas Jeszenszky, Klaus Weinrotter and Raimund Jurkowitsch, process for the production of cellulose carbamates, European patent application 0 178 292 A2, Int. Cl. ⁴ : C 08 B 15/06 , Priority: 09.10.84).

The published patent application DE 36 38 456 A1 describes examples of how carbamates, which are formed from sugars such as glucose or lactose in a urea melt, form within a few seconds (Dieter Ekkehard Autenrieth, Ge molten urea as a disintegrant for lignocellulosic raw materials and as a chemical Reaction partner for the polyols obtained during the digestion or for other polyols from other sources, published patent application DE 36 38 456 A1, Int. Cl. ⁴ : C 08 B 15/00, filing date: 11.11.86). Sugar such as B. glucose contain a semi-acetal OH group, which together with the carbon atom on which it is located is nothing more than a hidden aldehyde group - an aldehyde to which a molecule of water has first attached, after which one of the by Hydration resulting vicinal OH groups with the alcoholic OH group on the C atom in position 5 of the glucose molecule forms a semi-acetal ring with elimination of water, which is stable. The remaining OH group from the hydrated aldehyde is now called the semi-acetal OH group.

Formaldehyde can also form an analog structural element, e.g. B. if formaldehyde and urea react with each other:

H ₂ N-CO-NH ₂ + O = CH ₂ → H ₂ N-CO-N = CH ₂ + H ₂ O

H ₂ N-CO-N = CH ₂ + HOH → H ₂ N-CO-NH-CH ₂ OH.

This creates a hemiacetal, the hidden formaldehyde from which formaldehyde can also be released can (undesirable reaction when curing urea form aldehyde copolymer on which the "formaldehyde problem" is based). The methylol group contains an OH group of the same kind as e.g. B. in the semi-acetal structural element of the glucose molecule, to which isocyanic acid can add up very quickly, which Prerequisite for the technical usability of this carba Mat formation is when in the binary system made of solid urea and carriers of acidic OH groups in the hot press Iso Cyanic acid is caught so quickly and exhaustively that thereby the decomposition of urea in a first approximation subject to thermodynamic control by mass effect law is described.

With the help of the conversion of sugars in melted urine The addition of isocyanic acid can serve as a model reaction to all possible acidic OH groups in the hot press demon be treated. This is possible because the Iso cyanic acid equimolecular amount of ammonia used in the decomposition release of urea, does not simply escape, but quantitatively in the respective distillate under toluene or Xylene caught in the water separator and in the Des tillat can be quantified by titration and on Because of this happy fact, the key to ver of this kind of implementation. In addition, the  Reaction melts are saturated with ammonia from this outgassing what every time the sugar is converted into melted Urea creates the same energetic basis, so that the end measured the decomposition of urea only by concentration the isocyanic acid is controlled in the reaction mixture. The Concentration level of isocyanic acid in the reaction melt zen has the same meaning as the position of a valve in a water pipe. As long as the isocyanic acid by addition is consumed on semi-acetal OH groups and therefore their concentration is kept at a low level, decomposes urea, with isocyanic acid being supplied later. If this situation changes in the course of the implementation, hear the Decomposition of urea because of the concentration of iso cyanic acid increases in the reaction melt. Because with everyone Reactions of sugar in molten urea in the first place Approximation is actually such a simple and clear thermodynamically controlled system, these can (except for the implementation of the cane sugar).

During the first, slightly exothermic reaction phase, the Mass of outgassing ammonia, which with the distillates in the Template or the water separator is worn, directly per proportional to the mass of released isocyanic acid or Number of mole equivalents of immediately available of the semi-acetal OH groups which the isocyanic acid on take or the mass of decomposed urea.

If, in addition, urea is reversed in the reaction melts is set, this means that this additional mass Urea reacts intact with the sugar molecules. This actually happens, which can be seen from the fact that in the distillates water from condensation reactions and form amide or ammonium formate are included. More carbamic acid on the radiator, however, is due to the fact that at reaction times of several hours also normal alcohol lische OH groups add isocyanic acid, whereby at the same time more ammonia than expected is found in the distillate.  

Example 2 (No. 2)

Reaction conditions: 2½ hours under boiling p-xylene.

Example 3 (No. 3)

Reaction conditions: 6½ hours under boiling p-xylene.

Example 4 (No. 4)

Reaction conditions: 6 hours under boiling toluene.

Example 5 (No. 5)

Reaction conditions: 7½ hours under boiling p-xylene.

As can be seen from the following table, the implementation of monosaccharides and disaccharides in molten Urea at 100 ° -140 ° C usually 1 mole equivalent Ammonia formally released on 5 OH groups in the sugar concerned set. 1 mole of glucose (monosaccharide) gives 1 mole Ammonia, but 1 mole of milk sugar (disaccharide) only 1.6 Moles of ammonia corresponding to those contained in milk sugar 8 OH groups. Example 5 deviates from this finding. In the Implementation of the cane sugar is exactly half of the ammonia Get the same amount as with milk sugar.

This formal approach to getting started is thus founds that ammonia can only be left if previously generated isocyanic acid and then on OH groups is added. The Zer hears without consuming isocyanic acid from urea. There are 6 OH groups in sorbitol actually 6 molar equivalents of isocyan in the urea melt trap acid, leaving 6 molar equivalents of ammonia, which are registered as loss of mass, because in this case play ammonia is lost as a gas; Example 1.

The columns in Table 1 are numbered consecutively. The information in the columns marked in this way means:
Column 1: Example, No. . .
Column 2: molar amount of the sugar used (MS or DS) or of the sugar alcohol sorbitol and molar amount of the urea.
Column 3: Mass of the distillate in the water separator in g.
Column 4: density of the water-white distillate; δ = g / cm ³ .
Column 5: Ammonia produced in g; as a loss of mass in the case of sorbitol or in the distillate dissolved in the sugars.
Column 6 .: Ammonia produced in moles; as a loss of mass in sorbitol or in the distillate contained in the sugars.
Column 7: ammonia in% of the expected amount; for sugars (MS or DS) based on the rule found in the experiments.

Table 1

With the mono- and disaccharides, the completely different reak is based tion course compared to the conversion of sorbitol into ge molten urea in no way that the in the Sac Chariden also contained another alcoholic OH group Would have reactivity to isocyanic acid; rather be the different course of the reaction rests on semi-acetal and acetal structural elements in the saccharides, with to whom the implementation begins and then logically theirs Take course - very different from sorbitol. Here is the Difference in the chemical behavior of aldoses and ketoses not as pronounced as that between ordinary aldehydes and ketones. "The easy oxidizability of is remarkable Hydroxyl groups which are in the α-position to the oxo group. Therefore In contrast to the ketones, the ketoses also have a reduced effect ornamental, d. that is, the difference in chemical behavior of the Aldose and ketosis is not as pronounced as the one between Aldehydes and ketones ". For this reason semi-ketals and ketals no further from hemiacetals and acetals below divorced (see Hans Beyer, textbook of organic chemistry, 9th edition, p. 285, S. Hirzel Verlag LEIPZIG 1962).

"With the monosaccharides present in the lactol form basically two functionally different hydroxyl groups, the glycosidic (in aldoses at the C atom 1, in Distinguish ketoses at the C atom 2) and alcoholic ones. The glycosidic linkage of two sugar molecules to form the di Saccharide is therefore possible in two ways: once is done  the water leak between the two glycosidic hydro xylene (construction principle 1) and the other between a glycosi and an alcoholic hydroxyl (principle 2). in the in the first case one speaks of the dicarbonyl compound and im second from the monocarbonyl compound of the disaccharides. Both building principles, using the example of pipe and milk sugar to be illustrated differ in that the former is not reducing, but the second reduce works "(Hans Beyer, textbook of organic Chemistry, as above, p. 304).

In the urea melt saturated with ammonia, the Disaccharides with the absorption of ammonia in two mono saccharide cleaved. For this ammonolysis, 1 mol equivalent ammonia to be applied to the acetal Bridge between the two halves of the disaccharide repeal. During the ammonolysis of cane sugar (construction principle 1) is one at the start of the reaction in molten urea remarkably extensive induction phase. It lasts about 10 minutes under boiling xylene until it turns on catchy colorless reaction melt darkened. The In The production phase for cane sugar is therefore the longest, ver Same with the induction phases in all other investigations ten sugars because there are no semi-acetal ones in the intact cane sugar OH group is present immediately for the addition of Isocyanic acid would be available, like the one at Um setting of milk sugar (building principle 2) is the case. rhyme Milk sugar lasts only a few seconds for the induction phase, although under boiling toluene (bp 110.6 ° C) instead of under boiling p-xylene (bp. 138.4 ° C) is reacted. This does clearly that already intact milk sugar in the urine melt isocyanic acid is consumed and ammonia is left remains, which then causes ammonolysis without delay.

As soon as the disaccharides are split, they react detects monosaccharides with isocyanic acid to all semiacetal OH groups have turned into carbamate groups. In order to  is the first reak that lasts only a few seconds to minutes tion phase ended.

This extremely rapid formation of carbamates is the Prerequisite that carbamates technically as formaldehyde scavengers, especially in the production of plywood and chipboard can be used. When the aminoplast adhesive cures, what takes only a few seconds is released formaldehyde, and in this critical phase it must be at the place of its creation standing be intercepted. According to the invention, this becomes achieved that during this critical phase with carbamates, which are formed from compounds with acidic substances during the curing process Provide OH groups and isocyanic acid, released ter formaldehyde is immediately trapped. Mono and disaccha ride with semi-acetal OH groups or those quickly can provide semi-acetal OH groups, but also Full acetals react quickly with isocyanic acid and are on Because of quickly available carbamates as formaldehyde catcher suitable, the known disadvantages of intact Urea as a formaldehyde scavenger should be avoided. Suitable Compounds are made with urea as a binary reaction mixture used in the heat at the right time he provide required carbamates.

The carbamates of the monosaccharides change in the urine melt more. Using the example of the implementation of D-glucose in molten urea, the elimination process of carbamic acid, the attack of intact urea on the mono saccharide derivative and finally the release of formamide described so that the amount of distillate is explained.

The existence of carbamic acid is based on new For research results (Johan K. Terlouw and Helmut Schwarz, Amgew. Chem. 99 (1987), 829-839) as proven.

In solution and as a solid, D-glucose is cyclic Hemiacetal, as lactol before and namely 63% in the energetic favored β-D configuration and 37% as α-D-glucopyra  nose. Both diastereomeric D-glucopyranoses are in solution probably through the open chain aldehyde form with each other in balance. They are with the open chain aldehyde form tautomer; one speaks of an oxo-cyclo-tautomerism (cf. Hans Beyer, Textbook of Organic Chemistry, as above, p. 294).

The D-glucose is converted into molten urea in the form of D-glucopyranose. It is initiated by the fact that isocyanic acid attaches to the acidic semi-acetal OH group in Position 1 added.

Carbamic acid is eliminated in the heat. It is about thermal cis elimination, which is appropriate the classic UGAEV reaction takes place. "This pyrolysis is a monomolecular reaction, but it is the opposite to the E1 reaction not via free ions, but via a cy clical transition state, in the bond breaking and formation occur almost simultaneously. Due to the ring structure of the Transition state is also the steric course as cis (syn-) elimination determined "(author collective, organi cum, basic organic-chemical internship, reprint of the 15th,  revised edition, pp. 302-303, VEB German publisher of Sciences BERLIN 1977).

In this way, β-D-glucopyranose carbamate emerges first an enol that can be thought of as a vinylogous hemiacetal, which is in tautomeric equilibrium with the keto form.

With the formation of a carbonyl group, the molten one Attack urea intact there, using one mole equi valent water is released.

In a reaction sequence involving an AMADORI rearrangement starts, formamide is split off, a keto-imino ver bond remains, which polymerizes to a dark resin (cf. Hans Beyer, textbook of organic chemistry, as above, Pp. 287-288).  

From the enol that is tautomeric with the keto compound Formamide is split off.

When the D-glucose is converted into molten urea, 78.45 g of distillate with a density of δ = 1.104 g / cm ^{3 are} collected. 16.8 g of this have been determined as ammonia. The rest consists of water and formamide; Bp 111 ° C at 20 torr; δ = 1.1334 g / cm ³ , of which 1 mol equivalent are expected in each case. Accordingly, 1.64 g = 2.05% of the expected amount are missing. In addition, 60.85 g of carbamic acid are sublimed in the cooler; that's 99.68% of the expected amount. These experimental findings support the developed idea of the course of the reaction; see. Example 2 and Tables 1 and 2.

With milk sugar in the urea melt there are no ge extended the first reaction phase as with cane sugar, because after the Addition of isocyanic acid to the semiacetal OH group in the intact milk sugar 1 mole equivalent of remaining ammonia is available for ammonolysis right from the start.

Adding up equations 1, 2 and 3 gives:

No ammonia remains in the first reaction phase.

How D-glucose carbamate continues to react has been described.

Provide information on how the D-galactose hemaminal continues to react the experimental data that must be interpreted.

When 1 mol of milk sugar monohydrate is reacted in molten urea, 135 g of distillate with a density of δ = 1.140 g / cm ^{3 are obtained} in a water separator. This contains 26.96 g = 1.583 moles of ammonia. If 1 mol equivalent of water (18.016 g) and 2 mol equivalents of formamide (90.08 g) can also be detected in the distillate, 135.056 g of the expected amount have been reached. The somewhat increased density of the distillate obtained compared to the density of formamide (δ = 1.1334 g / cm ³ ) can be related to the fact that the formamide (bp. 111 ° C at 20 torr) when distilling off in a toluene tractor in the presence of water decomposes, forming formic acid (δ = 1.220 g / cm ³ ) or ammonium formate. As a result, however, the amount of ammonia that can be determined by titration, which originates solely from the conversion of milk sugar into molten urea, is hardly changed, because titration is carried out with methyl orange as an indicator, whose turnover range is between pH 3.2-4.4, so that acidic ammonium formate cannot affect the accuracy of the titration with hydrochloric acid.

Ammonium salts are volatile in the heat, being in the Gas phase as ammonia and undissociated acid.

According to the kinetic gas theory is given with one temperature is the average momentum of molecules different mass always the same; the following applies: I = m.v [g.cm/sec] = const., d. H. the diffusion rate v of the molecule varieties, their mass is inversely proportional. Based on it a method for the isotope separation of natural uranium.

In Example 4, the following Er can also be used in this way Apparently explain what the idea of the reaction process supports: In example 4 is at the end of the cooler below one attached funnel with a hose connection to one Water jet pump escaping gas. Im expiring Water from the water jet pump is little from the start Detectable ammonia with indicator paper. After about 1 hour Cooking on the reflux condenser suddenly shows the indicator paper an acidic pH that sinks to pH ∼ 3.0, but soon climbs to pH 4 and above, but no longer above pH 7.0 until the reaction is stopped. First the light diffuses Ammonia (MW 17.032) from the ammonium formate in the gas phase out of the cooler end, then the heavy formic acid follows (MG 46.03). In the air flow, both gases reach the one after the other Water jet pump and cause sharp concentration peak in the water flowing out of the water jet pump, see above that they can be proven with indicator paper.  

In accordance with the experimental findings, fol Gender reaction pathway proposed for D-galactose hemaminal:

D-galactose hemaminal reacts with intact urea, whereby 1 molar equivalent of ammonia is released.

The corresponding, substituted and thereby stabilized, open-chain aldimine is stored in one of the AMADORI levies analogue reaction.

The enol tautomeric to the keto compound is converted into a 6-ring mechanism formamide eliminated.

Due to the possible tautomerism, the keto-aldimin goes in the closed keto semi-aminal over. This becomes a provided acidic endiol, the immediately isocyan acid added, with 1 molar equivalent of ammonia from the Iso corresponding amount of urea remains.

Ammonamic acid produces carbamic acid and an enamine half aminal, the amount of ammonia just left remaining is needed. The enamine half aminal stands with the correspond the imin hemiaminal in tautomeric equilibrium; both can condense with each other, with 0.5 molar equivalents of ammonia to be released.

By ingesting 1 molar equivalent of water, the Condensate the open chain arrangement can be achieved.

After this versatile reaction sequence, which the Ammono Lysis of milk sugar carbamate in melted urea closes, remain at the end of the milk sugar monohydrate - except dark resinous polymerization and condensation products as a residue - 1.5 mol equivalents of ammonia in the distillate, 1 molar equivalent of water and 2 molar equivalents of formamide, or instead of water and 1 mole equivalent of formamide, 1 mole equivalent Ammonium formate left; together 133.65 g. Be on the cooler 2 molar equivalents = 122.09 g of carbamic acid expected.

The following were found in the distillate: 1.583 molar equivalents 26.96 g of ammonia, 1 mole equivalent of formamide and 1 mole equivalent Ammonium formate; together 135.06 g. The cooler has 134.0 g = 2.195 molar equivalents of carbamic acid sublimed.  

The 9.8% higher molar amount of carbamic acid in the cooler ent speaks well a 5.5% higher molar amount of ammonia. A Shortage of 0.112 molar equivalents = 1.91 g of ammonia plausible explanation due to inevitable loss due to Ab diffuse ammonia gas at the end of the cooler. More carbamic acid than expected makes it clear that addition of isocyanic acid normal, slightly acidic alcoholic OH groups, comparable to those in sorbitol, to a lesser extent.

Analysis of the conversions of fructose and cane sugar in ge melted urea.

The D-fructose is only known in the ß configuration. With Accordingly, isocyanic acid forms β-D-fructose carbamate, leaving 1 mole equivalent of ammonia.

Only the CH ₂ OH group can be claimed for the cis elimination of carbamic acid in a UGAEV reaction; see. the analysis of example 2.

This fructose derivative contributes to the resulting double bin an acidic OH group that acts as a vinylogous semi-acetal OH group can be understood and added accordingly  they also use isocyanic acid.

Enols and endiols are proton-active compounds that even Form ointment such as B. ascorbic acid. Therefore, enol esters are also to be regarded as mixed acid anhydrides.

A kind of AMADORI-Um goes well with the experimental results Storage of the so-called enol ester, the C = C double bond the role of a C = N double bond as in the classic AMADORI rearrangement.

The keto compound condenses with urea, 1 mol equivalent water is formed. After an AMADORI rearrangement creates a compound that formamide in the heat as Frag ment splits off.

The imino compound stabilizes to the amino compound - again in a kind of AMADORI rearrangement, so that a ver bond arises that can condense with itself, whereby after the condensation, 1 molar equivalent of water is present will be.

Thus the experimental results in Example 3 have an Er clarification found (see Tables 1 and 2). Except for the 18.952 g = 1.113 moles of ammonia, which was determined by titration is 36.032 g = 2 moles of water and 45.043 g = 1 mole of form amide or 18.016 g = 1 mol water and 63.059 g = 1 mol Ammo nium formate - a total of 100.027 g expected. Actually have the distillate is 97.0 g.  

The implementation of cane sugar in melted urea under differs from the implementations described so far Sugaring in that from the beginning in cane sugar - in disaccha rid according to building principle 1 (dicarbonyl compound of the disaccharides) there is no semiacetal OH group available, the iso Could rapidly intercept cyanic acid, which then becomes an equimolecular Amount of ammonia would remain.

In a urea melt, isocyanic acid reacts as an anion that isosteric with the stretched carbon dioxide molecule.

The proton released is taken up by ammonia (cf.

NH ₄ ^⊗ ⇄ H ^⊗ + NH ₃ pK _S value = 9.25

F. Seel, Fundamentals of Analytical Chemistry and Chemistry in aqueous systems, pp. 331-332, Verlag Chemie GmbH, Weinheim / Bergstr. 1955), so that initially in the urea melt Ammonium isocyanate with little ammonia in equilibrium located. The isocyanate anion can in turn be a base Pick up proton from a Frotonen-active OH group (acid). The quicker the more acidic such an OH group is. For this reason, semiacetal OH groups (which lead to Class of OH groups in the neighborhood of electronegatives Groups include), OH groups in enols and endiols as well phenolic OH groups easily with isocyanic acid.

The acidity of alcohols is usually very low (ethanol: K _S ≈ 10 ^-16 ; pK _S = - log K _S ≈ 16), but the acidity is significantly increased in the vicinity of electronegative groups. "For example, in tartaric acid HOOC-CHOH-CHOH-COOH, due to the accumulation of electronegative oxygen atoms, the hydroxyl groups are acidic enough to be methylated with diazomethane, which is not possible with normal alcoholic hydroxyl groups (HA Staab, introduction in theoretical organic chemistry, 4th edition, p. 618, Verlag Chemie GmbH, Weinheim / Bergstr. 1966) ".

As soon as in the π or charge transfer complex between the alcoholic OH group or between the more or less azide OH group and the isocyanate anion, the alcoholate anion and Having formed isocyanic acid, the alcoholate anion acts as Nucleophile on the C atom of isocyanic acid, which in their two mesomeric limit states with a positive charge on the C atom appears and in these limit states as carbenium ion is formulated.

Differences in the acidity of primary, secondary and tertiary alcohols are minor. Therefore, it cannot be expected that the isocyanate anion would preferentially attack a particularly acidic OH group at any point in this disaccharide when converting cane sugar into molten urea, especially since all the OH groups attached to it in the α-D-glucopyranose radical are equatorial to the pyranose ring are arranged in the armchair shape; in the β-D-fructofuranose residue, the two secondary OH groups occurring therein are in the trans position to one another and are each arranged in the trans position to one of the two CH ₂ OH groups, so that equivalence can also be assumed here.

Because inconsistent even before ammonolysis of cane sugar Cane sugar carbamate is the interpretation of the reaction ver runs when converting cane sugar into melted urine fabric not possible. It can only be peculiarities with the Cane sugar molecule and the monosaccharide contained therein ten are highlighted.  

It is striking that cane sugar in melted urea after 7.5 hours with boiling xylene only 13.51 g = 0.793 molar equivalents of ammonia in only 58.1 g of particularly high density distillate (δ = 1.165 g / cm ³ ) and 212, 6 g = 3.483 molar equivalents of carbamic acid; the latter represent the molar equivalents of isocyanic acid previously reacted. During the implementation, ammonia has been consumed and the stoichiometric balance remains missing.

For the ammonolysis, 1 mol equivalent of ammonia is to be added put. Another mole equivalent of ammonia can be found in the Fruc toserest have been included. After ammonolysis is namely the fructofuranose ring that is only stable in the glycoside, which is half of the cane sugar has become unstable the and has the residual vine to become stable in the fructopyranosis ring rearrangement (Hans Reyer, textbook of organic chemistry, as above, p. 297). The inevitable ring opening of the fructo furanose in the ammoniacal system can be the reason that 1 mole equivalent of ammonia with the intermediate occurring Keto group condensed, being an open chain fructose ketimine and 1 mole equivalent of water is formed.

How now the extent of the formation of formamide, which in the Reak tion of intact urea with the monosaccharide derivatives as Subsequent product arises and in the form of ammonium formate (from Water and formamide) for the high density of the distillate is responsible with the relatively small amount of Distillate to be agreed may not be plausible for the time being be explained.

In Table 2 below, the actual and he awaited yields of ammonia and carbamic acid, as well the expected amounts of water and formamide each he compared amount of distillate. Water and form amide can also partially in the form of ammonium formate Distillate, which is especially the case if the distillate in question has a relatively high density  points.

The columns in Table 2 are numbered consecutively. The information in the columns marked in this way means:
Column 1: Example, No. . .
Column 2: molar amount of the sugar used (MS or DS) or of the sugar alcohol sorbitol and molar amount of the urea.
Column 3: Mass of the distillate in the water separator in g.
Column 4: density of the water-white distillate; δ = g / cm ³ .
Column 5: Ammonia produced in moles (and g in brackets); recorded as mass loss in the case of sorbitol or in the distillate by titration recorded in the sugars.
Column 6: Based on the analysis of the reaction course expected mass of ammonia in moles (and g in brackets).
Column 7: Mass of carbamic acid sublimed in the cooler in moles (and g in brackets).
Column 8: Based on the analysis of the course of the reaction expected mass of carbamic acid in moles (and g in brackets).
Column 9: Based on the analysis of the reaction course expected mass of water in moles (and g in brackets).
Column 10: Based on the analysis of the reaction course expected mass of formamide in moles (and g in brackets).
Column 11: Based on the analysis of the reaction course expected mass of distillate in g.
Column 12: Difference column 11 - column 3 in g.
Column 13: Dark resinous residue in the reaction vessel in g.
Column 14: Total loss of mass in g, based on the molar amount of the sugar or sugar alcohol used in column 2. The monosaccharides D-glucose and β-D-fructopyranose as well as the sugar alcohol sorbitol have actually been converted in twice the amount given in this table; the same applies accordingly to the amount of urea used in Examples 1, 2 and 3.

example 1

Approach:
First, 500 g of an approximately 75% by weight aqueous sorbitol solution with toluene are boiled on a water separator until all the water has been removed. In this way, 138 g = 27.6% water is collected in the water separator within 3 hours.

362 g = 1.987 mol sorbitol remain in the flask; C ₆ H ₁₄ O ₆ ; MG 182,178 as a slightly yellow melt.

There are now 716.0 g = 11.922 moles of urea; H ₂ N-CO-NH ₂ ; MG 60.059 added and heated until everything has turned into a yellow homogeneous melt. This takes about 30 minutes.

First, in the toluene for 1 hour with the reflux condenser Boiled water separator. Only a few drops separate heavy distillate. Then the toluene is replaced by xylene replaced. It is then continued at about 140 ° C for 4 hours cooks. After this time, the ammonia development is almost full constantly stopped.

Intermediate yields: 144.8 g = 2.37 moles of carbamic acid in the cooler; HO-CO-NH ₂ ; MG 61,043 deposited. 753.8 g of a perfectly clear, red-brown oil remain in the flask.

Cooking in xylene continues for 2 hours. The melt tarnishes and turns brown. In the end, only a few gas rises blow up in the melt. The development of ammonia is practical table stopped.

Another 23.0 g of carbamic acid have settled in the cooler.

Exploit:
167.8 g = 2.75 moles of carbamic acid.
717.5 g sorbitol polyurethane as semi-solid honey.
192.7 g loss in mass due to outgassing ammonia.

Example 2

Approach:
600.6 g = 10 moles of urea: H ₂ N-CO-NH ₂ ; MG 60.059 are completely melted. In the clear, water-white melt, 360.32 g = 2 moles of D-glucose; anhydrous; C ₆ H ₁₂ O ₆ ; MG 180.16 resolved. The clear, bright reaction mixture is mixed with p-xylene; Sp. 138 ° C overlaid and brought to a boil. The reaction mixture turns yellow, then deep red and finally reddish brown.

After the reaction starts, the reaction is quite violent. The entire cooler area is occupied, and a current of heavy water-colored drops sink through in the water separator the submitted p-xylene. However, hardly any ammonia escapes, so that the radiator end abge with a loose cap can be covered. After about 2.5 hours of cooking, it begins to turn red to foam brown resin in the flask. At this time the separation of the distillate in the water separator almost opened hears and it is canceled.

Exploit:
121.7 g = 1.994 moles of carbamic acid as sublimate in the cooler.

156.9 g of a heavy water-white liquid; δ = 1.104 g / cm ³ , which contains ammonia in solution, have accumulated in the water separator. When titrated with n / 10 HCl against methyl orange, 307 mg of this consume 38.6 ml of n / 10 HCl (f = 1.7032 mg / ml) as a change indicator. Accordingly, 156.9 g of distillate contain 33.6 g = 21.415% ammonia; NH ₃ ; MG 17.032.

671.9 g of dark viscous resin remain in the flask.

The mass balance is 10.42 g missing.

Example 3

Approach:
6.00.6 g = 10 moles of urea; H ₂ N-CO-NH ₂ ; MG 60.059 are completely melted. In the clear, water-bright melt, 360.32 g = 2 moles of anhydrous D (-) - fructose; C ₆ H ₁₂ O ₆ ; MG 180.16 resolved. The initially yellow reaction mixture quickly turns deep red, then reddish brown. With p-xylene; Sp. 138 ° C is covered, then is boiled in a reflux condenser with Wasserab.

In the first 5 minutes after the reaction has started  the healing should be turned off because the reaction is like that violent that the full radiator capacity is used and Distillate at the cooler end threatens to leak. It escapes hardly any ammonia, so that with a loosely placed cap Cooler end can be covered.

After 4.5 hours, no heavy, colorless distillate is left about. It is still cooked for 2 more hours, with the Finally the dark product begins to foam in the flask. To A total of 6.5 hours of cooking is stopped.

Exploit:
There are 170.5 g = 2.793 moles of carbamic acid in the cooler and on the cap; HO-CO-NH ₂ ; MG 61,043 discontinued.

194.0 g of water-white distillate can be removed from the water separator; δ = 1.1496 g / cm ^{3 can be} drained. A sample of 333 mg of ammonia-containing distillate consumes 38.2 ml of n / 10 HCl when titrating with n / 10 HCl against methyl orange as a change indicator, which corresponds to 65.06224 mg NH ₃ (f = 1.7032 mg / l ). 194.0 g of distillate thus contain 37.904 g = 19.54% ammonia; NH ₃ ; MG 17.032.

604.5 g of dark viscous resin remain in the flask Contains traces of xylene.

Example 4

Approach:
480.5 g = 8 moles of urea; H ₂ N-CO-NH ₂ ; MG 60.059 are partially melted. Then 360.3 g = 1 mol of lactose monohydrate; C ₁₂ H ₂₂ O ₁₁ .H ₂ O; MG 360.32, which have been piled up on the urea, mixed with the melted. Ultimately, this creates a slightly yellow, clear, easily movable melt that suddenly changes color very quickly from reddish brown to dark brown.

With toluene; Sp 110.6 ° C is covered and ge for cooking brings. A colorless, heavy river separates from the start liquid that collects in the water separator. It escapes only a little ammonia, which is at the cooler outlet under a funnel, which is connected to a water jet pump via a hose  is suctioned off. After about 1 hour of cooking, the indi shows kator paper, moistened with running water from the Was jet pump even has an acidic pH value; pH ∼ 3! The pH soon climbs to pH 4 and above, but no more above pH 7 as at the beginning.

A thick coating of carbamic acid is formed in the cooler cold area sublimed. Lastly, with a wood chip the cooler should be kept open in one place to avoid that that there is overpressure in an apparatus that has become dense builds up.

After there is practically no product left in the water separator accumulates, the reaction is stopped; Cooking time 6 hours.

Exploit:
135.0 g of a water-bright liquid that contains a lot of ammonia in solution have accumulated in the water separator; δ = 1.140 g / cm ³ . By titrating with n / 10 HCl sweeping methyl orange as a change indicator, 92.65 mg of NH _{3 are} found in 464 mg of the distillate (1.7032 mg / ml × 54.4 ml = 92.65 mg). The distillate contains 19.97% ammonia; NH ₃ ; MG 17.032.

134.0 g = 2.1952 moles of carbamic acid; HO-CO-NH ₂ ; MG 61.043 balanced.

After decanting from toluene and drying at 100 ° C give 573.5 g of a red-brown resin, which at 100 ° C. is still flowable. This resin is in the drying cabinet Poured 100 ° C into a beaker, which takes several hours ert; Final resin weight: 567.0 g; Total loss: 4.79 g.

Example 5

Approach:
480.5 g = 8 moles of urea; H ₂ N-CO-NH ₂ ; MG 60.059 are completely melted. Then 342.3 g = 1 mol of sucrose; C ₁₂ H ₂₂ O ₁₁ ; MG 342.30 stirred with the melt, resulting in a water-bright, clear, easily movable reaction melt ent. With p-xylene; Sp. 138 ° C is covered, then boiled on a reflux condenser with a water separator. The reaction melt gradually changes color to yellow and orange after deep red boiling within 10 minutes. After 10 minutes of boiling, the continuous separation of colorless drops begins, which sink into the water separator. Hardly any ammonia escapes, so the radiator outlet is covered with a loose cap.

After 3.5 hours of cooking is interrupted because the cooler is almost is completely blocked with carbamic acid.

Intermediate yields:
45.9 g water-clear distillate in a water separator.

164.3 g = 2.69 moles HO-CO-NH ₂ ; MG 61.043 are weighed out in the cooler.

After cooling to room temperature, the p-xylene from the dunk poured resin. It is dried with compressed air. It stays 574.8 g of dark resin in the flask.

It is again boiled in p-xylene for 4 hours. in the A further 48.3 g of carbamic acid are deposited in the cooler. After ins A total of 7.5 hours of boiling in p-xylene is stopped.

Exploit:
212.6 g = 3.483 moles of carbamic acid as sublimate in the cooler.

58.1 g water white distillate; δ = 1.1645 g / cm ³ in the water separator. 337 t of the distillate use 46.0 ml n / 10 HCl = 78.3472 mg NH ₃ (f = 1.7032 mg / ml) when titrating with n / 10 HCl against methyl orange as a change indicator. Accordingly, 58.1 g of distillate contain 13.51 g = 23.25% ammonia; NH ₃ ; MG 17.032. A foamy, red-brown, brittle, readily water-soluble resin remains in the flask. It cannot be weighed out precisely because p-xylene remains trapped in the cavities. The resin is therefore dissolved in 450 g of water; Solution 984.7 g. 3.958 g of this solution lose 1.828 g = 46.185% water on drying. The solution contains 53.8% solid resin and 984.7 g solution 529.92 g solid resin. The mass balance shows a deficit of 22.18 g.

Urea-formaldehyde copolymer adhesive has the advantage that it is unbeatably inexpensive and because of its particularly quick Curing in the heat compared to other types of glue short cycle times during operation e.g. B. chipboard presses allowed.

When curing urea-formaldehyde copolymer adhesive becomes however released formaldehyde.

With the help of a binary reaction mixture one can now Prepare effective formaldehyde scavenger at the same time formed with the release of unwanted formaldehyde and this formaldehyde, which can otherwise be booked as a loss converted into valuable methylol groups, which like all the others Methylol groups with alcoholic OH groups, especially in Cellulose share of the substrate form ether bridges and the on this way even contributes to the adhesive force.

Such a binary reaction mixture consists of solid urine substance derived from the other component, the carrier of azides OH groups remains spatially separated until the urine Dissolve the fabric in the heat when pressing the glued substrate sets, producing isocyanic acid or ammonium isocyanate - the active reactant that with the acidic OH groups the other component as stated above within whole short time (a few seconds; depending on the acidity of the OH groups) forms carbamates, which in turn release them reacted formaldehyde and generate methylol groups and in this way the undesirable formaldehyde is even useful eliminate them.

Binary reaction mixtures, all solid urea than that contain a component can be manufactured by that solid urea ver with the carriers of acidic OH groups is mixed so that 2 phases remain in the mixture, one of which is solid urea. Solid urea  can e.g. B. with mono- and disaccharides with semiacetal OH groups and other carriers of OH groups in the neighborhood of electronegative groups such as tartaric acid or citric acid, but also with lactic acid on kieselguhr or silica gel and others suitable α-hydroxycarboxylic acids with or without inert carriers ger, but also z. B. with chloral hydrate; Mp 57 ° C, chloral half acetal and chloralammoniak, all typical representatives of Carriers of acidic OH groups in the vicinity of electronegatives Represent groups, be mixed.

Other binary reaction mixtures can be made from solid urea and suitable β-dicarbonyl compounds such as acetoacetic ester or Acetylacetone can be put together on an inert support. Such β-dicarbonyl compounds contain tautomeric equations always weighs more or less enol with an acidic OH group (see also Hans Henecka, chemistry of beta-dicarbonyl compounds, Organic chemistry in detail, published by Hellmut Bredereck and Eugen Müller, Springer Verlag BERLIN, GÖTTINGEN, HEIDELBERG 1950).

Solid urea can be mixed with an endiol such as without difficulty L (-) - ascorbic acid together to form the binary reaction mixture as an example of a representative of α-hydroxy carbonyl compounds, also called reductones or reductonates can be called, because they reduce only in the alkaline medium have an effect.

Azide OH groups can also be found in phenols. This addie also isocyanic acid, just like they do with diazo Let methane methylate. Such phenolic OH groups com in lignins and lignin degradation products and lignin building elements proposed to also binary with solid urea Have reaction mixtures or systems combined.

All of these binary reaction mixtures or systems are one thing in common: they only deliver carbamates in the heat, whereby  the necessary temperature also below the melting point of the pure urea, because the "contaminated" urine the normal melting point of 135 ° C in legal Way down according to the degree of "contamination" can be set. Sinters before carbamate formation the urea and finally forms a reaction melt with the carriers of acidic OH groups.

Especially at relatively low reaction temperatures the use of a catalyst is recommended. It is believed, that urea already under the action of ammonium chloride at temperatures well below its normal melting point (Mp. 135 ° C) in ammonium isocyanate.

The NH ₂ groups in the urea can be detached, which is used in the production of mixed carbonic acid diamides. Mixed carbonic acid diamides are obtained in the implementation of urea (preferably in excess) with the corresponding hydrochloride of primary amines, e.g. B. in the following reaction, which, however, is carried out in an aqueous medium.

H ₂ N-CO-NH ₂ + CH ₃ NH ₃ ^⊗ Cl ^⊖ → H ₂ N-CO-NHCH ₃ + NH ₄ ^⊗ Cl ^⊖ .

It stands to reason that in a sintering mixture of urea and ammonium chloride, the complex formed from both Reactants easily split off ammonia.

In this sequence of reactions, the catalyst, the ammonium chloride constantly regenerates, but the urea breaks down this process - as desired.

Claims (10)

1. A method for reducing the content of free form aldehyde in the production of chipboard and plywood with an aminoplast adhesive in a heated press, whereby in addition to the adhesive binary reaction mixtures of solid urea and at least one carrier of acidic OH groups is used are characterized in that in this process such reaction mixtures provide in the heat carbamates which immediately catch the formaldehyde also released in the heat when aminoplast adhesives are cured, formaldehyde reacting with the free amide functions in the carbamates and then reacting to each of them H atom is replaced by an advantageous methylol group. 2. The method according to claim 1, characterized in that a carrier of acidic OH groups with the solid urea, the is used in prilled or powdered form, as loose Batch is applied. 3. The method according to claim 1, characterized in that powdered urea with a carrier of acidic OH-Grup pen is intimately mixed, the mixture being mechanically rela tiv solid compacts or grains is used becomes. 4. The method according to any one of the preceding claims, characterized characterized in that the solid particles or grains with ammonium chloride in powder form, which serves as a catalyst be used. 5. The method according to claim 4, characterized in that Ammonium chloride, which serves as a catalyst, is indicated in the manner is used that it is molecularly dispersed or as its own phase in one or all of the constituents of the solid particles or grains  is included. 6. The method according to any one of claims 1 to 5, characterized ge indicates that as a carrier of acidic OH groups chemical Compounds are applied to the OH groups in the neighborhood of electronegative groups, e.g. B. semi-acetal OH groups in mono- and disaccharides; semiacetal and fully acetal OH groups in the vicinity of halogens such as i. B. in chloral hydrate and chloral hemiacetal; OH groups in α-hydroxy carboxylic acids such as. B. in tartaric acid or lemon acid; OH groups in α-hydroxy-carbonyl compounds (reducto nate or endiolates) such. B. in glyceraldehyde or in Dihydroxyacetone, but also in L (-) - ascorbic acid. 7. The method according to any one of claims 1 to 5, characterized ge indicates that as a carrier of acidic OH groups chemical Compounds are applied by keto-enol rearrangement such acidic OH groups can provide such. B. the ß-Di carbonyl compounds, e.g. B. acetylacetone or acetoacetic ester. 8. The method according to any one of claims 1 to 5, characterized ge indicates that as a carrier of acidic OH groups chemical Compounds containing phenolic OH groups applied are such. B. lignins, lignin components, e.g. B. Coniferyl alcohol or sinapinal alcohol and lignin degradation products such as B. Guaiacol. 9. The method according to any one of claims 1 to 8, characterized ge indicates that binary reaction mixtures are used come that additionally inert material or to be glued Contain substrate such. B. diatomaceous earth, zeolites, cage connection manure, wood flour or wood chips; which are suitable, liquid Include compounds with acidic OH groups or Verbin accumulations with acidic OH groups on the surfaces. 10. The method according to any one of claims 1 to 9, characterized ge indicates solid urea in particles or grains  on the ver with a carrier of acidic OH groups the substrate is sprinkled or mixed.