Oxidation of naphthene hydrocarbons in the presence of boron compounds

Borate-assisted liquid-phase selective oxidation of n-pentane

“…Based on these findings, it may be suggested that an alkyl metaborate is far more effective for directing the oxidation of n-pentane towards the formation sec-pentanols compared to an orthoborate and boric oxide. These observations agree with the findings of Itskovich et al [22], McMahon and Chafetz [56] and Illingworth [57], who investigated the oxidation of alkanes and cycloalkanes with various types of boron compounds, and reported that alkyl metaborates give better selectivity and less inhibition of the oxidation than trialkyl orthoborates and boric acid. The fact that s-BuMB gives better selectivity than the same concentrations of TiPrB and boric oxide can be explained by the higher Lewis acidity of alkyl metaborates compared to alkyl orthoborates and boric oxide [52,58,59].…”

“…One concept that has been reported for improving alcohol selectivity in alkane oxidations is the Bashkirov process, which involves the use of boron compounds such as boric acid, boric oxide and borate esters [17][18][19]. These boron species function as Lewis acids which direct the oxidation towards the formation of alcohols, and subsequently trap the alcohols in the form of borate esters to protect them from over-oxidation [20][21][22][23][24]. This idea formed the basis of several industrial-scale processes for the oxidation of cyclohexane to cyclohexanol/cyclohexanone, used as intermediate for the production of nylon-6, oxidation of cyclododecane to cyclododecanol/cyclododecanone used as intermediates for nylon-12, as well as the oxidation of C 10 -C 20 alkanes for the synthesis of higher aliphatic alcohols used in the manufacture of detergents and surfactants [20,25,26].…”

“…According to several investigators [22,[37][38][39][40], it has been suggested that during the borateassisted oxidation of alkanes, a coordinatively bonded complex is formed between the boron atom and unpaired electrons on the oxygen atom of the intermediate alkyl hydroperoxide, as illustrated in Scheme 3. The unstable complex may subsequently decompose homolytically into free radicals such as R 1 O • and HO • , which further propagate the oxidation, or it can undergo heterolytic decomposition resulting in the formation of molecular products, mainly alcohols.…”

“…Itskovich et al [22] estimated that only 10-15% of the overall decomposition of a hydroperoxide goes into the formation of free radicals. The main direction of hydroperoxide decomposition in the presence of boron compounds is through a non-radical path which substantially favours alcohol formation, and the lower level of free radicals explains the observed inhibition of the oxidation [41][42][43].…”