Patent GB-654166-A (GB)
Title: Process for making alkoxyacetals
Filed: 1947-10-25
Abstract: In the production of alkoxy acetals by reacting in the presence of boron trifluoride as catalyst a dialkyl acetal of an aldehyde containing at least two carbon atoms to the aldehyde molecule with an alkyl ether of an alpha, beta-unsaturated aliphatic alcohol, the sum of the carbon atoms in said aldehyde and said alcohol being at least five (see Group IV (b)), more than one mole of the vinyl ether may add to the dialkyl acetal to give a polyalkoxy acetal, thus an acetal R1CH2CH(OR2)2 would react with n moles of the vinyl ether CH2 : CHOR2 to form a polyalkoxy acetal <FORM:0654166/IV (a)/1> R1 being an alkyl, aryl or aralkyl group, R2 an alkyl group and n an integer, e.g. from 2 to 20.  In an example, mixtures of polyalkoxyacetals of the above type are obtained in addition to 1,1,3-triethoxyhexane when vinyl ethyl ether is added dropwise to an excess of diethyl butyral containing an ether solution of boron trifluoride with external cooling.  U.S.A. Specification 2,165,962 is referred to.ALSO:Alkoxyacetals are obtained by reacting in the presence of boron trifluoride as catalyst, a dialkyl acetal of an aldehyde containing at least two carbon atoms to the aldehyde molecule with an alkyl ether of an alpha, beta-unsaturated aliphatic alcohol, the sum of the carbon atoms present in said aldehyde and said alcohol being at least five, the product containing a straight chain of carbon atoms when the alcohol contains two carbon atoms and a branched chain of carbon atoms when the alcohol contains more than two carbon atoms. The reaction is preferably effected at 25 DEG  to 75 DEG  C. and the preferred catalyst is the complex compound of boron trifluoride and diethyl ether.  On completion of the reaction the catalyst is neutralized by adding an alkali such as sodium hydroxide, sodium carbonate or sodium bicarbonate. The alkoxy acetals may be converted to unsaturated aldehydes which may be reduced to saturated alcohols or they may be hydrolysed to alkoxy aldehydes which may be reduced or oxidized to the corresponding alkoxyalcohols or alkoxy acids, respectively. Hydrogenolysis of the alkoxyacetal may also be carried out to remove one alkoxy radical of the acetal group to form alkyl ethers of polyhydric alcohols and an alcohol corresponding to the alkoxy group of the acetal which is removed.  When a dialkyl acetal R1CH2.CH(OR2)2 is reacted with a vinyl ether CH2 : CH.OR2, where R1 is an alkyl, aryl or aralkyl radical, and R2 is an alkyl radical such as methyl, ethyl, propyl, butyl, amyl, hexyl, heptyl or octyl radical, the alkoxy acetal formed is R1CH2CH(OR2).CH2CH(OR2)2.  Whe a dialkyl acetal R1CH2CH(OR2)2 is reacted with an unsaturated ether R3CH : CHOR2 the alkoxy-acetal formed has the formula <FORM:0654166/IV (b)/1> where R1 is hydrogen or an alkyl, aryl or aralkyl radical and R2 and R3 are alkyl radicals, e.g. those specified above.  More than one mole. of the vinyl ethers may add to the dialkyl acetal to give a polyalkoxy acetal, thus an acetal of the formula R1CH2CH(OR2)2 would react with n moles. of the vinyl ether CH2 : CHOR2 to form a polyalkoxyacetal <FORM:0654166/IV (b)/2> wherein R1 is alkyl, aryl or aralkyl, R2 is alkyl and n is an integer, e.g. from 2 to 20.  In examples: (1) vinyl ethyl ether is added dropwise to an excess of diethyl butyral containing an ether solution of boron trifluoride-ether complex with external cooling. After neutralizing the catalyst with an excess of sodium carbonate the mixture is distilled to yield 1,1,3-triethoxyhexane which is identified by hydrolysis and de-ethanolation to 2-hexanal.  Some polyalkoxyacetals of the above type are also obtained; (2) vinyl ethyl ether and diethyl 2-ethylhexal (in excess) are reacted as in (1) yielding 1,1,3-triethoxy-4-ethyloctane; (3) ethyl 1-butenyl ether is added to an excess of diethyl acetal as in (1), yielding 1,1,3-triethoxy-2-ethylbutane; (4) vinyl ethyl ether is similarly reacted with diethyl hexal to yield 1,1,3-triethoxyoctane.  The product of (3) may be simultaneously hydrolysed and de-ethanolated to form alpha ethyl crotonaldehyde.  Normal amyl alcohol may be obtained from the alkoxy acetal obtained by reacting diethyl propional with vinyl ethyl ether.  U.S.A. Specification 2,165,962 is referred to. The Specification as open to inspection under Sect. 91 states that when dibutyl acetal is reacted with vinyl ethyl ether, 1,1,3-tributoxybutane and 1-ethoxy-1-butoxyethane are obtained together with a complex mixture of ethoxy- and butoxy-acetals. This subject-mater does not appear in the Specification as accepted.