Patent GB-722538-A (GB)
Title: Cyclic esters of boric acid
Inventor: GARNER PHILIP JAMES
IPC: C07F5/04
Filed: 1952-02-21
Abstract: The invention comprises as new compounds cyclic esters of boric acid of the general formula <FORM:0722538/IV (b)/1> wherein n represents 0 or 1, R represents a hydrogen atom or an alkyl, aralkyl, cycloalkyl, or aryl group and R1 is an alkyl, aralkyl, cycloalkyl or aryl group. The esters may be prepared by reacting, at elevated temperature the appropriate diol having the hydroxy groups on adjacent carbon atoms or on carbon atoms separated by one carbon atom with an alkyl, aralkyl, cycloalkyl or aryl ester of boric acid.  The preferred diols are the alkane diols such as the propane diols, butane-1,2(1,3- or 2,3-)-diol, pentane 1,2-diol and the corresponding 2,3- and 2,4-diols, hexane-1,2(2,3-, 2,4- or 3,4-)-diol, heptane 1,2- or 3,4-diol, octane-1,2-diol, and the corresponding 4,5-diol, 2,4-dimethylhexane-2,4-diol, 2,4 - dimethylpentane - 2,4 - diol, pinacol and 2-methylpentane-2,4-diol.  Specified aromatic substituted diols which may be employed are 1-, 2- or 3-phenylpropane-1,2-diol, 1-, 2- or 4-phenylbutane-1,2-diol and 1- or 3-phenylbutane-1,3-diol. The boric ester used is preferably a triester but mono- or di-esters may also be used. If a triester or diester is used it should preferably be derived from an alcohol or phenol capable of being removed readily from the reaction as it is formed, e.g. by simple or azeotropic distillation.  Specified esters are trimethyl, triethyl, tributyl, triphenyl and tricyclohexyl borates.  An esterification catalyst, e.g. sulphuric, p-toluene sulphonic acid or hydrogen chloride may be employed if desired.  An inert liquid diluent may also be present.  Another method of preparing the esters comprises esterifying with the appropriate alcohol or phenol, an acid ester of the general formula p  <FORM:0722538/IV (b)/2> wherein R and n are as defined above.  These acid esters may be made by esterification of boric acid with the appropriate diol, e.g. one of the diols specified above.  The alcohol or phenol may be an alkanol such as methanol, ethanol, a propanol, butanol, pentanol or homologue thereof, benzyl alcohol, phenylethyl alcohol, phenol or a cresol of xylenol or homologue thereof.  If desired an esterification catalyst may be present.  The esterification may be conducted by refluxing a mixture of the acid ester and the alcohol or phenol diluted with an inert solvent such as benzene, toluene or xylene under such conditions that water is removed from the system.  In examples: (1) ethyl 2,4-dimethylhexane-2,4-diol borate is obtained by distilling azeotropically a mixture of 2,4-dimethylhexane-2,4-diol and triethyl borate dissolved in benzene until the liberation of ethyl alcohol is complete; (2) ethyl pentane-2,4-diol borate is obtained from pentane-2,4-diol and triethyl borate by a similar procedure as in (1); (3), (4) and (5) ethyl-2,4-dimethylpentane-2,4-diol borate, ethyl pinacol borate and ethyl 2-methyl-pentane-2,4-diol borate respectively are obtained in a similar manner from the corresponding diol and triethyl borate; (c) 2-methylpentane-2,4-diol borate is refluxed with diisopropylcarbinol in the presence of toluene until water evolution is complete to yield diisopropyl-carbinyl 2-methylpentane-2,4-diol borate.  The 2-methylpentane-2,4-diol borate is prepared by refluxing 2-methylpentane-2,4-diol with boric acid and benzene until no more water is evolved.  The ester products may be used as additives in liquid fuels for internal combustion engines as described in Specification 722,537, [Group III].