GB2146016A - Method for the preparation of haloacetals and halodioxolanes - Google Patents

Abstract

A process for the preparation of haloacetals of the formula: <IMAGE> where X is chlorine or bromine and R' and R'' are the same and represent C1 to 5 aliphatic groups or R' and R'' together represent a 1,2-ethylene group, optionally substituted with 1 to 4 C1 to 3 alkyl groups, forming a dioxolane ring, is disclosed, in which vinylacetate and bromine or chlorine are added in simultaneous increments to C1 to 5 aliphatic alcohol while maintaining a constant slight excess of the halogen to form a haloacetaldehyde dialkylacetal which optionally is further reacted with an optionally substituted ethylene glycol in the presence of a strong acid to form a 2-halomethyldioxolane.

Description

SPECIFICATION Method for the preparation of haloacetals and halodioxolanes This invention relates to a process for the production of haloacetaldehyde dialkylacetals or cyclic acetals of the formula I:

where X is chlorine or bromine and R' and R" are each the same and are a lower aliphatic group of 1 to 5 carbon atoms or R' and R" together represent a 1,2-ethylene group which can be substituted by 1 to 4 alkyl groups having 1 to 3 carbon atoms and which is joined to the oxygen atoms to form a dioxolane ring.

The haloacetals above described, including the haloacetaldehyde aliphatic acetals where the aliphatic group is 1 to 5 carbon atoms in length, are described in U.S. Patent No. 2,411,826 which describes their synthesis by reacting a solution of vinyl acetate in alkanol with the requisite halogen which may be either chlorine or bromine. Example IV of this patent applied to the "methyl bromoacetal" (bromoacetaldehyde dimethylacetal) provided yields of about 46%. The diethyl acetal equivalent (Aldrich Chemical Co &num;12,398-6 (1981-82)) was obtained in 68% yield. This prior patent also describes the halogenation of vinyl acetate followed by reaction thereof with ethylene glycol to provide a product noted as the "chloracetal of ethylene glycol" boiling at about 1500C. This may or may not be the dioxolane.The synthesis of the halomethyl dioxolanes is described by Filachione (the named inventor of U.S. Patent No. 4,211,925) in JACS 61, 1705-06 (1939). Here a yield of 83% is reported for the chloroacetaldehyde diethylacetal when the process was carried out at very low temperature by cooling with a dry ice-acetone mixture. With the application of the same conditions chloroacetaldehyde dimethylacetal and bromoacetaldehyde dimethylacetal were obtained in yields of 53% and 46%, respectively. When the process was carried out at -10 to -5 C the yield of chloroacetaldehyde diethylacetal decreased to 70%.

The acetals of this invention, particularly the haloacetaldehyde dimethyl and diethyl compounds and the halomethyl dioxolanes are useful intermediates in the preparation of "safeners" or "antidotes" against the actions of certain well-known and commonly used selective herbicides. The herbicide antidotes are described including their synthesis, in U.S. Patent No. 4,269,775, issued May 26, 1981. These antidotes are commercially useful, requiring the haloacetals to which this invention is directed, in better yields and purity than afforded by the prior art processes to make use of these antidotes agriculturally viable. The preferred compounds of these antidotes are based upon the halomethyl dioxolane intermediate.

It is an object of this invention to provide the haloacetaldehyde dialiphatic acetals and the related halomethyl dioxolanes in good yields and high purity.

This invention is based on the discovery that the haloacetaldehyde dialiphatic acetals are obtained in much higher yields than those of the afore-mentioned prior art due to the simultaneous incremental addition of the halogen and vinyl acetate to the alcohol.

When, as in the prior art, the vinyl acetate is all added at the beginning, it is decomposed by hydrolysis and polymerization during the addition of the halogen. This causes formation of by-products which were difficult and cumbersome to separate.

Further, it has been found that the dioxolanes of the formula I are best prepared by cross acetalization of the haloacetaldehyde dialkylacetals of the formula I obtained by reacting chlorine or bromine and vinyl acetate with an aliphatic alcohol. This cross acetalization is achieved by reacting the haloacetaldehyde dialkylacetals with an optionally substituted ethylene glycol in the presence of a strong acid.

Direct reaction of ethylene glycol with vinyl acetate and halogen provides poor yields (under 50%) and is very difficult to purify. In the two-stage process of this invention via halodialiphatic acetal formation and cross acetalization with the arylsulfonic acid catalysts provides yields in excess of 90% and purity of 98%.

Accordingly, the present invention provides a process for preparing the haloacetals of the fomula I which process comprises (a) adding vinyl acetate and halogen at a temperature of from -10 to 20"C in simultaneous increments to an aliphatic alcohol having 1 to 5 carbon atoms with the halogen in slight excess during the addition to form the haloacetaldehyde dialkylacetals of the formula I in which R' and R" are each the same and are a lower aliphatic group of 1 to 5 carbon atoms and (b) reacting the haloacetaldehyde dialkylacetals obtained in step a) with an ethylene glycol which can be substituted by 1 to 4 alkyl groups having 1 to 3 carbon atoms in the presence of a strong acid to form the 2-halomethyldioxolanes of the formula I in which R' and R" together represent a 1,2-ethylene group which can be substituted by 1 to 4 alkyl groups having 1 to 3 carbon atoms.

In step a) the excess of halogen during the addition of vinyl acetate and halogen as a rule amounts to 2 to 20 mole %, preferably 5 to 10 mole %. This requirement can easily be met by observing the coloring of the reaction mixture imparted by the halogen. Upon completion of the incremental addition, any ex cess of halogen is titrated and neutralized by vinyl acetate.

Within the temperature range of -10 to 20"C temperatures from -5 to 0 C are preferred.

The aliphatic alcohol used in step a) may be selected from the group of alcohols such as methanol, ethanol, propanol, isopropanol, butanol, isobutanol, sec. butanol, tert. butanol and pentanol. If the hal oacetaldehyd dialkylacetals obtained in step a) are further reacted to dioxolanes the preferred alcohol to be used in step a) is methanol. The selection of the halogen, X, is determined by the degree of reactivity desired in the further steps of synthesis for which the specific acetals and dioxolanes are prepared ac cording to this invention.

After completion of the reaction of step a) the reaction mixture is diluted with a low boiling halogen ated solvent, such as methylene chloride, chloroform, carbon tetrachloride and 1,2-dichloreothane, and the resulting solution is washed with water to remove the hydrogen halide (HX). The desired acetal is then recovered from the solution by distillation or it may be utilized directly in solution.

The reaction of step b) can be performed at a temperature of from 0 to 50"C, preferably 10 to 40"C.

After completion of the reaction the reaction mixture can be worked up in the same manner as described for step a). As strong acids which catalyze the cross acetalization of step b) there can be used sulfuric acid, phosphoric acid, hydrogen chloride or, preferably, an arylsulfonic acid, such as p-toluenesulfonic acid. These acids are used, as a rule, in amounts of less than 5% by weight of the ethylene glycol. Nor mally the afore-mentioned acids are used in amounts of 0.01 to 0.1 mole per mol of haloacetaldehyde dialkyiacetal of the formula I. The preferred acid in the presence of which the cross acetalization is car ried out is p-toluenesulfonic acid.

Appropriate ethylene glycols which can be used according to the invention are, for example, ethylene glycol, 1 ,2-propanediol, 1 ,2-butanediol, 1,2-pentanedioi, 2,3-butanediol, 1 ,2-dihydroxy-1 -methylpropane and pinacol. Among these diols ethylene glycol is preferred.

The invention will be more specifically described in its preferred mode in the following Examples wherein both the bromo- and chloroacetaldehyde dimethyl acetals are directly prepared and where these compounds are also utilized to prepare the bromoethyl dioxolane and the chloromethyl dioxolane. It should be noted that these procedures are exemplary and that variation in temperatures and pressures, as recognized by those skilled in the art, may be required to prepare the haloacetals with other aliphatic alcohols.

Example 1: Bromoacetaldehyde dimethylacetal To a 2 litre cooled flask is added 320 gm (10 moles) methanol. The methanol is cooled to 0 C and 172.2 gm (2 moles) vinyl acetate and 320 gm (2 moles) bromine are added simultaneously over two hours. The bromine is maintained in a small excess at all times as observed by the coloring of the solution. The temperature is held between 0-10 . When all the material is added and the color neutralized by vinyl acetate, the cooling is removed and the batch is left overnight.

To the cooled batch, 250 ml of methylene chloride and 250 ml of water are added and stirred. The stirring is stopped and the organic layer separates below the water layer. The organic layer is removed and the water layer is extracted with 100 ml additional methylene chloride. The extracted organic layers are combined. The low boiling solvent and by-products are distilled at atmospheric pressure. Vaccum is then applied and 14.3 gm bromoacetaldehyde (5.8%) distills at 600C/100 mm Hg. Bromoacetaldehyde dimethylacetal (202 gm. 86.4 % yield) is obtained at 80"C1133 mbar (purity 99 %). Since the bromoacetaldehyde is recycled and utilized in subsequent batches, the total yield of bromoacetaldehyde dimethylacetal is equivalent to 92.4 %.

Example 2: Chloroacetaldehyde dimethylacetal The procedure of Example 1 is followed but chlorine (141.6 gm) is used instead of the bromine. The chlorine is introduced below the liquid surface in the flask by dip tube. The yields of chioroacetaldehyde dimethylacetal (B.P. 129-130"C) and chloroacetaldehyde are about 1.5 % lower than the equivalent compounds of Example 1.

Example 3: 2-Bromomethyl dioxolane To a cooled 2 litre flask is charged 320 gm (10 moles) methanol. The contents are cooled to about -5"C.

Over a period of about two hours, 172.2 gms (2 moles) of vinyl acetate and 320 gms (2 moles) of bromine are charged. The bromine is kept in slight excess of observing the color of the solution. When the addition is completed and the slight excess of bromine is titrated with vinyl acetate, the mixture is permitted to come to room temperature (about 20"C) and is held overnight. Then the mixture is recooled to 0-10"C and charged with 250 ml of methylene chloride and 250 ml of water and stirred for about hour. Then the layers are permitted to separate. The bottom organic layer is separated and the water layer is extracted with two 100 ml portions of methylene chloride. The organic layers are combined.

The combined organic solution containing methylene chloride contains, in addition to the bromodimethyl acetal, some free bromoacetaldehyde, methanol and methyl acetate.

A 500 ml distillation flask, equipped with a vacuum fractionation column and head is charged with 128 gm (2.1 mole) ethylene glycol and 5 gm of p-toluenesulfonic acid. The organic layer is slowly added to the flask as it is heated. With brine cooling the condenser, methylene chloride, methyl acetate and methanol begins distilling at an overhead temperature of about 40"C. This phase of the distillation is continued until all the organic layer is introduced into the flask. Heating of the flask continues until the pot temperature reaches 100"C at which point vacuum is slowly applied. The pot temperature is kept at 100 120 C. The bromomethyl dioxolane distills at about 100 C/53 mbar.Some ethylene glycol distills with the product and is separated by cooling to about 0 C. As this glycol layer contains about 25 % by weight of bromomethyl dioxolane, it is recycled to the next batch.

Upon completion of the distillation, 100 ml of methylene chloride is added to the flask and refluxed for about 20 minutes and then cooled. The cooled reflux material is extracted with 50 ml of water.

The water layer is removed. The remaining organic layer contains the bromomethyl dioxolane held up in the column and is recycled to subsequent batches.

The yield (with allowances for the recycle) is about 90 % with 98-99% purity.

Example 4: 2-Chloromethyl dioxolane Following the procedure of Example 3, but substituting 141.6 gm of chlorine for the bromine yields 90 + % of 2-chloromethyl dioxolane (98 + % purity) distilling at 100"C/133 mbar.

Claims (13)

1. A process for the production of haloacetaldehyde dialkylacetals or cyclic acetals of the fomula I

where X is chlorine or bromine and R' and R" are each the same and are a lower aliphatic group of 1 to 5 carbon atoms or R' and R" together represent a 1,2-ethylene group which can be substituted by 1 to 4 alkyl groups having 1 to 3 carbon atoms and which is joined to the oxygen atom to form a dioxolane ring, which process comprises a) adding vinyl acetate and halogen at a temperature of from -10 to 20"C in simultaneous increments to an aliphatic alcohol having 1 to 5 carbon atoms with the halogen in slight excess during the addition to form the haloacetaldehyde dialkylacetals of the formula I in which R' and R" are each the same and are a lower aliphatic group of 1 to 5 carbon atoms and b) reacting the haloacetaldehyde dialkylacetals obtained in step a) with an ethylene glycol which can be substituted by 1 to 4 alkyl groups having 1 to 3 carbon atoms in the presence of a strong acid to form the 2-halomethyldioxolanes of the formula 1 in which R' and R" together represent a 1,2-ethylene group which can be substituted by 1 to 4 alkyl groups having 1 to 3 carbon atoms.

2. A process according to claim 1, wherein during the addition of vinylacetate and halogen the excess of halogen amounts to 2 to 20 mole %.

3. A process according to claim 1, wherein during the addition of vinylacetate and halogen the excess of halogen amounts to 5 to 10 mole %.

4. A process according to claim 1, wherein the addition of vinylacetate and halogen is performed at a temperature of from -5 to 0 C.

5. A process according to claim 1, wherein the reaction of the haloacetaldehyde dialkylacetals obtained in step a) with the ethyleneglycol is performed at a temperature of from 0 to 500C.

6. A process according to claim 1, wherein the reaction of the haloacetaldehyde dialkylacetal obtained in step a) with the ethyleneglycol is performed at a temperature of from 10 to 40"C.

7. A process according to claim 1, wherein sulfuric acid, phosphoric acid, hydrogen chloride or ptoluenesulfonic acid is used in step b).

8. A process according to claim 1, wherein p-toluenesulfonic acid is used in step b).

9. A process according to claim 1, wherein the strong acid in step b) is used in an amount of from 0,01 to 0,1 mole per mole of haloacetaldehyde dialkylacetal of the formula I.

10. A process according to claim 1, wherein there is used in step b) an optionally substituted ethyleneglycol selected from ethyleneglycol, 1,2-propandiol, 1,2-butanediol, 1,2-pentanediol, 2,3-butanediol, 1,2dihydroxy-1-methylpropane and pinacol.

11. A process according to claim 1, wherein there is used in step b) ethyleneglycol.

12. A process for the production of acetals of formula I substantially as described with reference to any of the Examples.

13. Acetals of formula I when produced by a process claimed in any of the preceding claims.