CS268280B1 - Process for preparing 4-oxopentylalkanoates - Google Patents

Abstract

The invention relates to a method for preparing 4-oxopentyl alkanoates of the general formula I, where R is hydrogen or alkyl of carbon number C, to C,. A solution of an allyl alkanoate of the general formula II, where R is H or alkyl of carbon number C-] to C, in a 5 to 100 molar excess of acetaldehyde is irradiated at temperatures of 5 to 30 °C with ultraviolet radiation.

Description

The invention relates to a process for preparing 4-oxopentylalkanoátů pattern of I, wherein R - is hydrogen or an alkyl group having carbon number ₁ to C ^ C.

4-Oxopentylkanoates, especially 4-oxopentyl acetate (I, R-CH 2), are one of the intermediates used in organic synthesis to prepare? 5-hydroxy-2-pentanone, which is the starting material for the production of drugs, vitamin B 1 and azo initiators used for the synthesis of telechelium polymers.

Conventional processes for the preparation of 4-oxopentylalkanoates of the formula I, in particular 4-oxopentyl acetate (I, R-CH2) and 4-oxopentyl formate (I, R-H), rely on the warm rearrangement of 3- (2-hydroxyethyl) -. Of 2,4-pentanedione formed by hydroxyethylation of 2,4-pentadione (Huet J., Druex J .: Compt. Rend. 258, 4570 (1964)) or on catalytic hydrogen-2-methylfuram in aqueous acetic anhydride (Rakhimkulov λ. G. and collaborators: USSR 0.. 0 1 020 425 (1983 /), further on the thermal decomposition of the editing compound and resulting from the reaction of 2-hydroperoxy-2-methyltetrahydrofuran and diacetyl or with glyoxal (Glukhovtsev VG et al .: Ser. Khim. 2, 485 (1977), Zh. Org. Khim. Vinogradov et al .: Izv. Akad. Nauk SSSR / 1969 / ζ Zh. Prlkl. Khim .: / Leningrad / £ 6, 467/1983 /).

Said processes for the preparation of the 4-oxopentylalkanoates of the general formula I generally represent several-step syntheses, often starting from relatively inaccessible substances. The chemical yields of the alkanoates of the formula I are less than 60% and must be separated from the by-products resulting, for example, from the decomposition of the initiator used.

These drawbacks are eliminated by a process for preparing 4-oxopentylalkanoátů of formula I wherein R is hydrogen or an alkyl group having carbon number ₁ to C according to the invention. Its essence lies in the fact that ee a solution of an allylalkanoate of general formula II, wherein RH or alkyl of carbon number up to C 2, in a 5 to 100 molar excess of acetaldehyde, is irradiated at ultraviolet radiation at temperatures of 5 to 30 ° C. A sufficiently high molar ratio of acetaldehyde: allyl alkanoate II guarantees a high yield of 1: 1 adducts, i.e. 4-oxopentylalkanoates of formula I at the expense of the formation of by-products of the addition of 1: n telomers of formula III, where RH or alkyl of carbon up to an - 2. After irradiation, the reaction mixture is worked up by distillation or rectification.

The effect of the process according to the invention is that the photochemically initiated radical addition of acetaldehyde to the allylalkanoates of the formula III produces 4-oxopentyl acetates of the formula I in relatively high yields. simple and easy to carry out the free radical addition itself, good separation of the reaction products of general formula I from the 1: n telomeres of general formula III and from the by-products formed by photolysis of acetaldehyde and the possibility to regenerate excess acetaldehyde.

The process according to the invention is further described in several exemplary embodiments.

Example 1 '

A solution of allyl acetate (25.8 g, 0.26 mol) in acetaldehyde (340.8 g, 7.74 mol) was irradiated in a photochemical reactor under a nitrogen atmosphere with a 400 W high pressure mercury lamp for 7 hours. The temperature of the reaction mixture was kept between 15 and 17 ° C by cooling the lamp. By first rectifying the reaction mixture, unreacted acetaldehyde was distilled off. Rectification under reduced pressure gave 29.8 g (80%) of 4-oxopentyl acetate (I, R-CH 2), b.p. 91-94 ° C (1.3 kPa, the structure of which was confirmed by elemental analysis, IR, NMR and mass Distillation of the residue gave 10.3 β (8.2%) of 7-acetoxy-4-ethoxyxy-2-heptanone (III, R 2 CH 2) b.p. 138-140 ° C / 66.6 Pa. The lower boiling fraction (13.4 g), b.p. 74-85 ° C / 1.3 kPa, showed the presence of 2,5-dihydroxy-2,3,5,6-tetramethyl-1,4-dioxane by mass spectroscopy. 3-hydroxy-3-methyl-2,4-hexanedione, 2,3-butanediol, 3-acetoxy-2-butanone and 3,4-dihydroxy-3,4-dimethyl-2,5-hexanedione, which are products of photolysis acetaldehyde.

Example 2

A solution of acetaldehyde (391.7 g, 8.89 mol) and allyl acetate (17.8 g, 0.178 mol) was irradiated for 8 hours with a high pressure 400 W mercury lamp at 20 ° C under argon. Rectification of the reaction mixture after removal of the acetaldehyde gave 22.3 g (87%) of 4-oxopentyl acetate (I, R @ CH3), b.p. 96-105 ° C / 1.6 kPa.

Example 3

A solution of allyl formate (38.8 g, 0.45 mol) and acetaldehyde (399.5 g, 9.07 mol) was irradiated in a photochemical reactor for 7.5 hours under a nitrogen atmosphere with a 400 W mercury lamp. Excess acetaldehyde was then distilled off from the reaction mixture, followed by rectification to give 38.1 g (65%) of 4-oxopentyl formate (I, R <H>), b.p. 90-93 DEG C./2 kPa, and 4.9 g (10% 7-formyloxy-4-formyloxymethyl-2-heptanone (III, RH) with a boiling point of 160-165 ° C / 0.3 kPa. '

Claims (1)

SUBJECT V Y N X L E Z U Process for the preparation of 4-oxopentylalkanoates of general formula I, wherein R - hydrogen or alkyl of carbon numbers C ₁ to C 1-4, characterized in that a solution of allylalkanoate of general formula II, wherein R H or alkyl of carbon numbers C ₁ to C 5 to 100 molar excess of acetaldehyde is irradiated with ultraviolet radiation at temperatures of 5 to 30 ° C.