Alkyl-branched Fatty Compounds: Hydro-alkylation of Non-activated Alkenes with Haloalkanes Mediated by Ethylaluminum Sesquichloride

Abstract

The general method for the cationic hydro-alkyl addition to the nonactivated C=C double bond of alkenes mediated by ethylaluminum sesquichloride (Et₃Al₂Cl₃) has been importantly improved and simplified by using haloalkanes (primary, secondary, tertiary) instead of alkyl chloroformates as alkylating agent and performing the reaction without any additional solvent. The protocol is especially suited to perform the hydro-alkylation of internal double bonds. Reaction of the haloalkane with Et₃Al₂Cl₃ gives an alkyl cation which is added to the alkene; hydride transfer from Et₃Al₂Cl₃ to the adduct carbenium ion gives the saturated addition product. Primary halo alkanes give the same addition product as the respective secondary halo alkane because of 1,2-H shift yielding the secondary carbenium ions. In the case of 1-alkenes triethylsilane has to be used as additional hydride donor to avoid di- and oligomerization. Special interest has been focused on alkylation of unsaturated fatty compounds, which are important renewable feedstocks, mostly (Z)-configured such as methyl oleate, high oleic sunflower oil, neopentyl glycol dioleate, but also (E)-configured i. e. dimethyl (E)-icos-10-enedioate, and with terminal double bond such as methyl 10-undecenoate. The respective alkyl branched fatty compounds were obtained after simple work-up with excellent to good yields. The protocol was scaled up without problems to > 0.5 mol.

Practical Applications The synthesis of alkyl-branched fatty compounds is of high importance since they have interesting properties that make them attractive for use in the cosmetics and lubricant area. We developed an industrially feasible method for the synthesis of well-defined alkyl branched oleochemicals.

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