Several alk-l-enyl alkyl ethers were obtained during preparative gas chromatography of acetals derived from saturated and unsaturated fatty aldehydes and methyl, ethyl, propyl and butyl alcohols. Analysis of these substituted vinyl ethers by argentation chromatography, gas-liquid chromatography, infrared spectroscopy, nuclear magnetic resonance spectroscopy and mass spectrometry showed that they were a mixture of cis and trans isomers. Aluminum metal was found to catalyze the decomposition of the acetals to the corresponding alk-l-enyl alkyl ethers. The cis-trans percentage composition was influenced by column characteristics, as well as by the alcohol moieties of the acetals, but the aldehyde moieties of the acetals had no influence.
The decomposition of the dimethyl acetals ofhexadecanal and cis, cis-l,9octadecadienal to the corresponding alk-l-enyl methyl ethers during gasliquid chromatography on fl-cyclodextrin acetate (fl-CDX acetate) and ethylene glycol succinate-phosphoric acid (EGSP) columns was recently reported by us1). The formation of a vinyl ether linkage (--O--CH=CH--) as a result of this decomposition suggested the possible existence of cis and trans isomers. It is the purpose of this paper to describe (a) factors which catalyze this decomposition, (b) separation and characterization of the cis and trans isomers of the alk-l-enyl ethers and (c) influence of column characteristics and alcohol moieties of the acetals on the cis-trans percent composition of these compounds.
Methods
Dimethyl acetals of aliphatic aldehydes were prepared by reacting the aldehydes with absolute methanol in presence of 100~ sulfuric acid at --30 Β°C and subsequent neutralization with methanolic potassium hydroxide solution as described previously2). The acetals derived from hexadecanal and ethanol, propanol and butanol were prepared essentially by the same procedure except that the methanol was replaced by the appropriate alcohol