Alkyl metaborate esters

Main group elements and organic compounds have catalytic activity in epoxidation with activated oxidants. They could be alternatives to catalysts containing expensive or toxic transition metals. The earliest work was carried out with fluorinated acetone, alkyl metaborate esters, and organic derivatives of arsenic and selenium (Fig. 1.2a-d) (Table 1.8). 

Alkyl metaborate esters in combination with organic hydroperoxides are reported to be active for epoxidation [182]. The borate esters are cyclic and have general formula (ROBO)3, where R is an alkyl group like cyclohexyl (CeHn). They are six-membered ring compoimds formed from O-B units with a pendant RO, and are 1 1 dehydro adducts of alcohol and boric acid. 

Any alkyl metaborate ester can be used cyclohexyl metaborate is easily prepared and is soluble in organic solvents. 

The general formula for boric acid esters is B(OR)2. The lower molecular weight esters such as methyl, ethyl, and phenyl are most commonly referred to as methyl borate [121 -43-7] ethyl borate [130-46-9J, and phenyl borate [1095-03-0] respectively. Some of the most common boric acid esters used in industrial appHcations are Hsted in Table 1. The nomenclature in the boric acid ester series can be confusing. The lUPAC committee on boron chemistry has suggested using trialkoxy- and triaryloxyboranes (5) for compounds usually referred to as boric acid esters, trialkyl (or aryl) borates, trialkyl (or aryl) orthoborates, alkyl (or aryl) borates, alkyl (or aryl) orthoborates, and in the older Hterature as boron alkoxides and aryloxides. CycHc boric acid esters, which are trimeric derivatives of metaboric acid (HBO2), are known as boroxines (1). 

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