EP0048251A1 - A process for the preparation of difunctional aldehydes - Google Patents

Abstract

Alkylation of dialkylaldehydes (Alpha), (Alpha) with organic dihalides in two or three phase systems in the presence of alkali and a phase transfer catalyst. Depending on the reaction conditions and the structure of the dihalides, bifunctional aldehydes having the formula I or II or their mixtures are obtained. (FORMULA) In which Z is an alkylyl, alkenylyl, aryldialkyl or cycloalkylyl structure and R1 and R2 are alkyl groups having 1 to 6 carbon atoms, and X is a halogen atom. These compounds can be used as starting materials for the synthesis of monomers. The aldehyde group can be converted into an alcohol, acid, amine or isocyanate function. The halogen atom can be converted to a hydroxy or amino group.

Description

A process for the preparation of difunctional aldehydes.

Difunctional compounds like diacids or diols having two indentical functional groups or aitiinoacids having different functional groups find an extensive use as monomers in the polymer industry.

We have studied the posibility to make difunctional aldehydes, that is compounds with two aldehyde func¬ tions or one aldehyde function and one halide func¬ tion.

The aldehyde group is of considerable chemical interest as an intermediate for acetals, alcohols, acids, esters, amines or isocyanates. However, aldehydes with a hydrogen atom in the α-position to the formyl group easily undergo undesired self- condensation reactions.

No simple method for the preparation of difunc¬ tional aldehydes (Fig. 1) without hydrogen atoms on the α-carbon atom has yet been described in the literature.

R, R,

Fig. 1 where Z is an alkylyl, alkenylyl, aryldialkyl or cylcoalkylyl structure and R, and R₂ are alkyl groups with 1-6 carbon atoms, and x is an halide atom. We have now found a simple method for preparing such difunctional aldehydes by alkylation of isobutyr- aldehyde, 2-ethylhexanal and similar aldehydes con¬ taining one α-hydrogen atom only, with different dihalides. We obtain the corresponding dialdehydes, but can if desired instead isolate the intermediary formed monoaldehyde-monohalide.

The process now developped is run under so called phase transfer catalysis (PTC) conditions, but the general PTC conditions e.g. used by Dietl and Brannock (Tetrahedron Letters no 15, s. 1273-1275, 1973) , Purohit and Subramian (Chemistry & Industry 16 Sept. 1978, s. 731-732) and US Patent no 4069258 in the preparation of monoaldehydes were found of little use in this case as they generally gave a lower yield of the desired difunctional aldehydes.

We have now however been able to modify the standard procedures as shown below to give difunctional aldehydes in good yields.

We can show the efficiency of our method in that it permits the use of non activated dihalides like 1,4- dichlorobutane as alkylating agents . Hitherto only activated halides such as allylchlorides and benzyl- chloride have been successfully used (cf litterature references above) .

We found a new problem in the preparation of difunctional aldehydes namely that the alkylation takes place not only at the C-atom of the aldehyde but also at the O-atom (Fig. 2) . R, R,

R, R, vinylether

Fig.

This undesired side reaction has not earlier been observed in the alkylation of isobutyraldehyde. It will cause a larger problem in the case of difunctio¬ nal aldehydes than in monofunctional aldehydes as a product O-alkylated in one end and C-alkylated in the other is totally unacceptable although it has reacted as desired to 50 % (Fig. 3) .

R, R.

Fig. 3

The present invention describes an alkylation of aldehydes containing only one hydrogen atom at the α-carbon atom using alifatic or aralifatic dihalides as alkylating agents under PTC-conditions. As a catalyst we use quaternary ammonium- or phosphonium salts. As base we use alkali hydroxides and/or carbonates.

Alkylation of said aldehydes by dihalides is a consecutive reaction where one halogen atom is replaced by the aldehyde before the other ^R2 ^R2

^Rl ^Rl

^Rl ^Rl ^Rl ^Rl

+ Nax + H₂0 Thus the reaction always passes a stage where one halide and one aldehyde group is present in the molecule. We have isolated these compounds and they can as well as the dialdehydes be used in the manu¬ facture of industrially important compounds li^'ke difunctional halide-aldehydes, halide-acids, halide- alcohols, halide-amines or halide-esters. Compare the use of aminoacids in the nylon manufacture.

Although there is a formal similarity between alkyla- tions using monohalides and dihalides, the dihalides do not give dialdehydes in good yields using the processes earlier described in the literature (see above) . The reaction rate is diminished during the reaction and the amount of selfcondensation and 0- alkylations products from the aldehyde, which is a major problem, is increased. We have unexpectedly been able to solve these problems by removing the aqueous .phase containing halide ions during the reactions and adding a fresh alkali solution.

The partition of the catalyst between the aqueous and organic phase is dependent on the lipophilicity of the cationic part of the catalyst and anions present in the system. A certain amount of catalyst will thus be removed with the aqueous phase and must be replaced.

Instead of an aqueous alkaline phase a solid phase consisting of hydroxides or carbonates or mixtures of the two can be used.

As hydrolysis or elimination of the halide causes a larger problem in the case of dihalides than mono¬ halides it has been found advantageous to use less nucleophilic bases like carbonates.

Exemple 1.

1,4 phenylene dipivalaldehyde

32 g of 50 % aqueous sodium hydroxide were heated to 70 in a 250 ml round-bottomed flask equipped with a reflux condenser, stirrer and bottom outlet. 0.78 g of tetrabutylammonium iodide in 30 ml of toluene was added. At a rate of 10 ml per hour the half part of a warm solution of 17.5 g of p-xylylyl chloride, 18 g of isobutanal in 20 ml of toluene was added. 40 ml of water of 50 C were added. Stirring was stopped. The two layers were allowed to separate and the aqueous phase discarded. Another portion of 32 g of 50 % aqueous sodium hydroxide and 0.38 g of tetrabutyl¬ ammonium iodide were added_.. The remaining half of the xylylyl chloride, isobutanal, toluene solution was dosaged as above. Finally 0.76 g of tetrabutyl¬ ammonium iodide was added and the mixture was stirred for 90 minutes at 70 C. 50 ml of water were added and the aqueous layer was removed. The organic layer was washed with three times 25 ml of water. The solvent was removed in vacuo. The residue was washed with 20 ml of ether at 0 C. After filtering the formed precipitate was washed with 5 ml of ether. 14.5 g of 1.4 phenylenedipivaloyl aldehyde was recovered m.p. 109-112 C decomp. After recrystallization the m.p. is 120-121°C.

The corresponding oxime has a m.p. of 167-169 C. After oxidation of the dialdehyde we obtained a diacid, m.p. 223-224°C (lit. 217°C) . After reduction of the dialdehyde we obtain 1.4-xylylyl-bis-2.2- dimethylethanol, m.p. 111-112 C.

O PI Example 2 .

6-chloro-2.2-dimethylhexanal

120 g of a 50 % aqueous solution of sodium hydroxide and 100 g of 1.4-dichlorobutane was heated to 70 C. 2.2 g of trioctylmethylammonium chloride dissolved in 27 g of 1.4-dichlorobutane were added. At a rate of 10 ml per hour 24 g of isobutyraldehyde were introduced. After one hour of additional stirring at 70°C 60 ml of water was added. The layers were sepa¬ rated and the aqueous phase removed. The organic layer was washed three times with water and dried over sodium sulfate. Unreacted 1.4-dichlorobutane was distilled off and a main fraction of 24 g was collec¬ ted at 72-96°C/9 mm Hg. By a fractional distillation of this product 6-chloro-2.2-dimethylhexanal (C- alkylated product) was separated from l-(4-chloro- butoxy) 2-methylpropene (0-alkylafced byproduct) . Their structures were determined by their IR- and masspectrum.

Exemple 3 .

6-chloro-2.2-dimethyl hex-4-ene-l-al

100 ml of water, 276 g of potassium carbonate, 70 ml of benzene and 5 g of tributylhexadecyl phosphonium jodide were heated to 70 C in 1 liter round bottomed flask equipped with a reflux condenser, stirrer and bottom outlet. During four hours a mixture of 50 g of 1.4 dichlorobutene-2, 72 g of isobutanal and 44 ml of bensene were added.Then 200 ml of water were added and the phases were separated. An new amount of 276 g of potassium carbonate in 100 ml of water and 2.5 g of catalyst was added to the organic phase and stirred 3.5 h at 70°C. 200 ml of water was added, the layers were separated and the organic phase washed with three times 100 ml of water.

After drying with sodium sulfate, the organic layer was distilled. 20 g of 6-chloro-2.2-dimethyl hex-4-ene-l-al were collected at 72-83 C at 5 mm Hg.

The structure was determined by IR and NMR and chlorine analysis.

Claims

We claim:

A process for the manufacture of difunctional aldehydes of the general formula

R₂ ^R2 ^Ri where Z is an alkylyl, alkenylyl, aryldialkyl or cykloalkylyl structure and R, and R_ are alkyl groups with 1-6 carbon atoms, and x is an halide atom, characterized in that aldehydes containing one hydrogen atom at the α-carbon atom

^Rl

R₂

where R, and R₂ are alkyl groups with 1-6 carbon atoms are alkylated by substituted or unsubsti- tuted, saturated or unsaturated alifatic, or aralifatic dihalides in the presence of alkali and a quaternary ammonium or phosphonium salts.

2. A process according to claim 1, characterized in that the reaction is carried out in a two- or three phase system, consisting of an organic, an aqueous and/or a solid alkaline phase.

3. A process according to claim 1 and 2 characterized in that the alkaline phase is removed and replaced by a fresh alkaline phase and an additional amount of the quaternary catalyst.