PROCESS FOR PRODUCING 2,2-DIALKYL-3-ACYLOXYPROPANALS

Abstract

A process for preparing an aldol ester of the formula (I), wherein at least one carboxylic anhydride of the formula (II) is reacted with at least one aldol of the formula (III) with heating in the presence of a basic catalyst with a pKa of the conjugate acid of at least 8, and the reaction product obtained from the process. The process provides a light-coloured and low-odour reaction product which has a high content of aldol ester content of the formula (I) and can be used, without elaborate purification steps, particularly without overhead distillation of the aldol ester, as a blocking agent for primary amines. The resultant blocked amines have a long storage life together with polymers containing isocyanate groups, and cure rapidly and reliably on contact with moisture to form mechanically high-grade and robust elastomers.

Claims

1. A method for preparing an aldol ester of the formula (I), ##STR00011## where R.sup.1 and R.sup.2 are identical or different alkyl radicals having 1 to 4 carbon atoms or together are an alkylene radical having 4 to 6 carbon atoms, and R.sup.3 is an optionally halogenated hydrocarbyl radical having 1 to 17 carbon atoms, wherein at least one carboxylic anhydride of the formula (II) ##STR00012## is reacted with at least one aldol of the formula (III), ##STR00013## optionally in the form of an oligomer thereof, while heating in the presence of a basic catalyst having a conjugate acid pKa of at least 8.

2. The method as claimed in claim 1, wherein R.sup.1 and R.sup.2 are each methyl.

3. The method as claimed claim 1, wherein R.sup.3 is an alkyl radical having 1 to 7 carbon atoms or is phenyl.

4. The method as claimed in claim 1, wherein the basic catalyst has a conjugate acid pKa of at least 9.

5. The method as claimed in claim 1, wherein the basic catalyst is triethylamine.

6. The method as claimed in claim 1, wherein it is executed at a temperature within a range from 80 to 150° C.

7. The method as claimed in claim 1, wherein it is executed without using an organic solvent or entraining agent.

8. The method as claimed in claim 1, wherein the aldol of the formula (III) is used as constituent of a reaction mixture obtained from the reaction of formaldehyde, optionally in the form of paraformaldehyde or trioxane, with at least one aldehyde of the formula (IV) ##STR00014## in the presence of a basic catalyst having a conjugate acid pKa of at least 8.

9. The method as claimed in claim 1, wherein it is executed in two stages, wherein (i) in the first step, the basic catalyst and formaldehyde are initially charged, then at least one aldehyde of the formula (IV) ##STR00015## is added in stoichiometric excess in relation to formaldehyde at a temperature within a range from 60 to 90° C., resulting in the formation of the aldol of the formula (III), after which volatiles are removed from the reaction mixture, and (ii) in the second step, the reaction mixture thus obtained is reacted with the carboxylic anhydride of the formula (II) at a temperature within a range from 100 to 130° C., wherein volatiles are removed from the reaction mixture during and/or after the reaction.

10. A reaction product obtained from the method as claimed in claim 1, wherein it comprises 60% to 95% by weight of aldol ester of the formula (I) and 5% to 40% by weight of other esters, aldehydes and/or acetals not corresponding to the formula (I).

11. The reaction product as claimed in claim 10, wherein it comprises triesters of the formula (V) and/or acetals of the formula (VI), ##STR00016##

12. A blocked amine obtained from reacting the reaction product as claimed in claim 10 with at least one amine that has a primary amino group and additionally at least one reactive group selected from primary amino group, secondary amino group, and hydroxyl group.

13. The blocked amine as claimed in claim 12, wherein the amine is selected from the group consisting of hexane-1,6-diamine, 1-amino-3-aminomethyl-3,5,5-trimethylcyclohexane, 4(2)-methylcyclohexane-1,3-diamine, 1,3-bis(aminomethyl)cyclohexane, 1,4-bis(aminomethyl)cyclohexane, 1,3-bis(aminomethyl)benzene, cyclohexane-1,2-diamine, cyclohexane-1,3-diamine, cyclohexane-1,4-diamine, bis(4-aminocyclohexyl)methane, 2,5(2,6)-bis(aminomethyl)bicyclo[2.2.1]heptane, 3(4),8(9)-bis(aminomethyl)tricyclo[5.2.1.0.sup.2,6]decane, α,ω-polyoxypropylenediamine having an average molecular weight Mn within a range from 170 to 500 g/mol, trimethylolpropane- or glycerol-started tris(ω-polyoxypropylenamine) having an average molecular weight Mn within a range from 330 to 500 g/mol, 1,4-phenylenediamine, 3,5-diethyl-2,4(6)-tolylenediamine, 2-(2-aminoethoxy)ethanol, 2-(2-(2-aminoethoxy)ethoxy)ethanol, and 3-aminomethyl-3,5,5-trimethylcyclohexanol.

14. A polyurethane composition comprising at least one polyisocyanate and/or polymer containing isocyanate groups and at least one blocked amine as claimed in claim 12.

15. A method comprising using the polyurethane composition as claimed in claim 14 as adhesive or sealant or coating.

Description

EXAMPLES

[0183] Working examples are presented hereinbelow, the purpose of which is to further elucidate the described invention. The invention is of course not limited to these described working examples.

[0184] “Standard climatic conditions” (“SCC”) refer to a temperature of 23±1° C. and a relative air humidity of 50±5%.

[0185] Unless otherwise stated, the chemicals used were from Sigma-Aldrich Chemie GmbH.

[0186] Description of the Measurement Methods:

[0187] Gas chromatograms (GC) were measured within a temperature range from 60 to 320° C. at a heating rate of 15° C./min and a 10 min hold time at 320° C. The injector temperature was 250° C. A Zebron ZB-5 column was used (L=30 m, ID=0.25 mm, dj=0.5 μm) at a gas flow of 1.5 ml/min. Detection was by flame ionization (FID). For assignment of GC peaks to chemical structures, a mass spectrum (EI.sup.+) was additionally recorded.

[0188] Infrared spectra (FT-IR) were recorded as neat films on a Bruker Alpha Eco-ATR FT-IR instrument. Absorption bands are reported in wavenumbers (cm.sup.−1).

[0189] DSC (differential scanning calorimetry) analyses were determined on a Mettler Toledo DSC 3+ 700 instrument in a temperature range of 10 to 400° C. with a heating rate of 4 K/m in using adiabatic M20 pressure crucibles (from T.Math.V Sûd, Switzerland) (first run).

[0190] The amine value (including blocked amino groups) was determined by titration (with 0.1N HClO.sub.4 in acetic acid against crystal violet).

[0191] Preparation of Aldol Esters of the Formula (I):

Example 1

Preparation of the Inventive Reaction Product Comprising 2,2-dimethyl-3-acetoxypropanal in the Presence of Triethylamine

[0192] Step 1 (Aldol Reaction):

[0193] A V4A steel reactor equipped with addition, stirring, heating, and cooling system and a distillation column with condenser and maintained under an atmosphere of nitrogen was charged with 297 kg of triethylamine (from BASF), 587 kg of paraformaldehyde (from Tennants Fine Chemicals), and 282 kg of deionized water and this was mixed. The mixture was heated under reflux to 60° C. with stirring. Into this was then metered 1523 kg isobutyraldehyde (from BASF) over a period of 3 hours, during which the reaction mixture was maintained under reflux at 65 to 75° C. After a further 30 min at reflux, no more exothermicity was discernible. The system was then switched over to distillation, the internal pressure was gradually reduced, and the volatiles were distilled off, firstly at 85° C./250 mbar and then at 100° C./50 mbar. 705 kg of distillate was collected (which according to gas chromatography was unreacted isobutyraldehyde, water, and a substantial part of the triethylamine). Remaining in the reactor was 1924 kg of reaction mixture, which according to gas chromatography comprised approx. 88% by weight of 2,2-dimethyl-3-hydroxypropanal (retention time approx. 3.2 min) and approx. 4% by weight of triethylamine (retention time 2.2 min).

[0194] Step 2 (Esterification):

[0195] The reactor was then brought to standard pressure with nitrogen, brought to reflux, and the internal temperature increased to 110° C. The internal pressure was then reduced to 250 mbar and 2076 kg of acetic anhydride (from BP Chemicals) added and mixed in over a period of 1 hour. This was then followed by removal of volatiles from the reaction mixture. For this, the reactor was set to fractional distillation (80% reflux) and the contents distilled at an overhead temperature of approx. 78° C. As soon as the overhead temperature reached 80° C., the internal pressure in the reactor was gradually reduced further and distillation each time continued until the overhead temperature again reached 80° C. Once the overhead temperature had exceeded 80° C. at an internal pressure of 30 mbar, the distillation, i.e. the removal of volatiles from the reaction mixture, was ended. A total of 2134 kg of distillate was collected (which according to gas chromatography was unreacted acetic anhydride, acetic acid, triethylamine, and 2,2-dimethyl-3-acetoxypropanal). The reaction product was then cooled and maintained under a nitrogen atmosphere.

[0196] 1851 kg of a clear, pale yellowish liquid with a mildly fruity odor was obtained. The reaction product comprised according to gas chromatography approx. 78% by weight of 2,2-dimethyl-3-acetoxypropanal (retention time 4.8 min), approx. 5.7% by weight of triesters of the formula (V) (retention time 10.9 min), and approx. 6.3% by weight of acetal of the formula (VI) (retention time 6.4 min and 6.6 min). This is hereinafter referred to as “reaction product from example 1”.

[0197] FT-IR: 2973, 2938, 2877, 2818, 2716, 1728, 1473, 1374, 1228, 1160, 1118, 1040, 892, 775.

[0198] A DSC of the reaction product was recorded, which is shown in FIG. 1. Weak exothermicity of 20 kJ/kg in the region from 105 to 155° C. was determined.

[0199] Purification of the reaction product by overhead distillation: (as comparison) 500 g of the reaction product obtained from example 1 was distilled under reduced pressure at 120 to 130° C. in a round-bottomed flask with distillation column. This yielded 370.4 g of distillate (=overhead-distilled 2,2-dimethyl-3-acetoxypropanal from example 1) at an overhead temperature of 84 to 87° C., 30 mbar and 60% reflux, which according to gas chromatography comprised approx. 94% by weight of 2,2-dimethyl-3-acetoxypropanal.

[0200] The first fraction (=first runnings) of 73.8 g was collected at an overhead temperature of 76 to 80° C., 30 mbar, and 80% reflux. This comprised according to gas chromatography approx. 56% by weight of 2,2-dimethyl-3-acetoxypropanal, approx. 17% by weight of acetic acid, and approx. 18% by weight of triethylamine. Left behind as a residue was 55.8 g having a content of 2,2-dimethyl-3-acetoxypropanal of 0.8% by weight.

Example 2: (Comparative)

Preparation of 2,2-dimethyl-3-acetoxypropanal in the Presence of Acid

[0201] A round-bottomed flask with distillation column and water separator was charged under a nitrogen atmosphere with 100 g of cyclohexane, 144.0 g of paraformaldehyde, 403.7 g of acetic acid, and 6.3 g of p-toluenesulfonic acid and mixed. The mixture was heated under reflux to 60° C. with thorough stirring and to this was slowly added 346.4 g of isobutyraldehyde such that the internal temperature did not rise above 75° C. The system was then switched from reflux to water separation and heated gradually to an internal temperature of 100° C. Once the internal temperature had reached 100° C., the internal pressure was gradually reduced, making sure that the internal temperature was maintained at about 100° C. At an internal pressure of 600 mbar, 81 g of water was separated. The system was then switched from water separation to distillation and the internal pressure reduced further, such that the internal temperature was maintained at about 100° C. At an internal pressure of 30 mbar and an overhead temperature of 67° C., the excess acetic acid was mostly removed. The reaction product was cooled and maintained under a nitrogen atmosphere. The distillate collected consisted according to gas chromatography mostly of cyclohexane, a little water, isobutyraldehyde, and acetic acid.

[0202] 576 g of a dark-colored liquid with a pungent odor was obtained. The reaction product comprised according to gas chromatography approx. 61.7% by weight of 2,2-dimethyl-3-acetoxypropanal (retention time 4.8 min).

[0203] A DSC of the reaction product from example 2 was recorded, which is shown in FIG. 2. Strong exothermicity of 530 kJ/kg in the region from 100 to 400° C. was determined.

[0204] Preparation of Blocked Amines:

[0205] Aldimine A1: (from the Inventive Reaction Product)

N,N′-Bis(2,2-dimethyl-3-acetoxypropylidene)-3-aminomethyl-3,5,5-trimethylcyclohexylamine

[0206] A round-bottomed flask was charged under an atmosphere of nitrogen with 373.0 g of the reaction product from example 1 comprising approx. 78% by weight of 2,2-dimethyl-3-acetoxypropanal. To this was then added with thorough stirring 170.3 g (1 mol) of 3-aminomethyl-3,5,5-trimethylcyclohexylamine (Vestamin® IPD, from Evonik), after which volatiles were removed at 80° C. and a vacuum of 10 mbar. This yielded 497 g of a clear, pale yellowish, low-viscosity liquid with a mildly fruity odor and an amine value of 223 mg KOH/g, which corresponds to a calculated aldimine equivalent weight of 252 g/equiv.

[0207] Aldimine R1: (Comparison, from Purified Reaction Product)

[0208] N,N′-Bis(2,2-dimethyl-3-acetoxypropylidene)-3-aminomethyl-3,5,5-trimethylcyclohexylamine

[0209] A round-bottomed flask was charged under an atmosphere of nitrogen with 293 g of overhead-distilled 2,2-dimethyl-3-acetoxypropanal from example 1. To this was then added with thorough stirring 170.3 g (1 mol) of 3-aminomethyl-3,5,5-trimethylcyclohexylamine (Vestamin® IPD, from Evonik), after which volatiles were removed at 80° C. and a vacuum of 10 mbar. This yielded 418 g of a clear, almost colorless, low-viscosity liquid with a mildly fruity odor and an amine value of 262 mg KOH/g, which corresponds to a calculated aldimine equivalent weight of 214 g/equiv.

[0210] Moisture-Curing Polyurethane Compositions:

[0211] Compositions Z1 and Z2

[0212] For each composition, the following constituents were mixed in a centrifugal mixer with the exclusion of moisture until a macroscopically homogeneous liquid had formed:

[0213] 213.7 g of a polymer containing isocyanate groups and having an NCO content of 3.7% by weight, based on a polyoxypropylenediol having an OH value of 56 mg KOH/g and toluene diisocyanate (Desmodur® T 80 P, from Covestro), 61.3 g of crosslinker (Desmodur® L67 MPA/X, from Covestro), 73 g of plasticizer, 149 g of solvent, 19 g of thickener, 417 g of inorganic filler, and 0.5 g of salicylic acid. To this was additionally added 67.7 g of aldimine A1 in the case of composition Z1 or 57.5 g of aldimine A1 in the case of composition Z2.

[0214] Each composition was stored in a tightly closed metal container with the exclusion of moisture and finally tested as follows:

[0215] The viscosity was determined using a Rotothinner at 20° C.: “freshly” refers to the measured viscosity 24 h after production of the composition. “4 w 40° C.” and “8 w 40° C.” refers to the viscosity after storage for respectively 4 weeks and 8 weeks at 40° C. in closed containers.

[0216] The curing rate (“BK drying time”) was determined under standard climatic conditions using a Beck-Koller drying time recorder in accordance with ASTM D5895. The results for phase 2 correspond to the skin-over time (tack-free time) of the composition.

[0217] Through-curing was determined by applying the composition in the form of a cylinder of 40 mm diameter and 4 mm height, allowing it to stand in standard climatic conditions (SCC) or at 5° C./80% relative humidity, cutting this open after 24 h or 48 h, and measuring the thickness of the cured layer that had formed on the surface of the composition. The results are reported as “24 h SCC” and “48 h SCC” and “48 h 5° C.”, according to the curing time and climatic conditions. For determination of the mechanical properties, a two-layer cured film was produced for each composition. This was done by applying a first layer in a thickness of 800 μm with a doctor blade and storing for 24 h in standard climatic conditions, followed by a second layer applied with a doctor blade in a thickness of 400 μm at an angle of 90° relative to the first layer. This two-layer film was stored in standard climatic conditions for a further 24 h, followed by 24 h in an air-circulation oven at 60° C. After a further 24 h in standard climatic conditions, strip-shaped test specimens of 100 mm length and 25 mm width were punched out of the film and used to determine the tensile strength and elongation at break in accordance with DIN EN 53504 at a strain rate of 180 mm/min and with a track length of 60 mm.

[0218] The appearance was determined optically on the film produced for the determination of mechanical properties.

[0219] The odor was determined by smelling through the nose, at a distance of about 100 mm, a freshly applied flat composition of about 150 mm diameter.

TABLE-US-00001 TABLE 1 Properties of compositions Z1 and Z2. Composition Z1 Z2 (comparison) Viscosity [mPa .Math. s] freshly 1800 1950 4 weeks 40° C. 2200 2400 8 weeks 40° C. 2350 2500 BK drying time phase 2 1:38 1:30 [h:min] phase 4 2:53 3:00 Through-curing 24 h SCC 2.6 2.6 (mm depth) 48 h SCC 3.9 4.0 48 h 5° C. 3.8 3.8 Tensile strength [MPa] 5.59 5.50 Elongation at break [%] 328 260 Appearance matt, nontacky, matt, nontacky, no bubbles no bubbles Odor mild, solvent- mild, solvent- like, slightly like, slightly fruity fruity

[0220] It can be seen from Table 1 that the inventive reaction product from example 1 is of excellent suitability as is, i.e. without further purification by overhead distillation, for the preparation of aldimine A1, which is used as a blocked amine/latent curing agent in a one-component moisture-curing composition. Composition Z1 in some cases surprisingly even exhibits better properties than composition Z2, which comprises aldimine R1 derived from 2,2-dimethyl-3-acetoxypropanal purified by overhead distillation. In particular, composition Z1 shows especially lower viscosity, even after storage, and especially high elongation, remaining properties being otherwise comparable.

[0221] Compositions Z1 and Z2 are suitable in particular as coating or covering, in particular as so-called liquid applied membrane for the sealing of roofs, bridges, terraces, etc.