Oxidations by the system "hydrogen peroxide manganese(IV) complex acetic acid" - Part II. Hydroperoxidation and hydroxylation of alkanes in acetonitrile

Higher alkanes (cyclohexane, n-pentane, n-heptane, methylbutane, 2- and 3-m ethylpentanes, 3-methylhexane, cis- and trans-decalins) are oxidized at 20 degrees C by H2O2 in air in acetonitrile (or nitromethane) solution in the presence of the manganese(IV) salt [L2Mn2O3](PF6)(2) (L = 1,4,7-trimethyl-1 ,4-7-triazacyclononane) as the catalyst. An obligatory component of the rea ction mixture is acetic add. Turnover numbers attain 3300 after 2 h, the yi eld of oxygenated products is 468 based on the alkane. The oxidation afford s initially the corresponding alkyl hydroperoxide as the predominant produc t, however later these compounds decompose to produce the corresponding ket ones and alcohols. Regio- and bond selectivities of the reaction are high: C(1) : C(2) : C(3) : C(4) approximate to 1 : 40 : 35 : 35 and 1 degrees : 2 degrees : 3 degrees is 1 : (15-40) : (180-300). The reaction with both. is omers of decalin gives (after treatment with PPh3) alcohols hydroxylated in the tertiary positions with the cis/trans ratio of similar to 2 in the cas e of cis-decalin, and of similar to 30 in the case of trans-decalin (i.e. i n the latter case the reaction is stereospecific). Light alkanes (methane, ethane, propane, normal butane and isobutane) can be also easily oxidized b y the same reagent in acetonitrile solution, the conditions being very mild : low pressure (1-7 bar of the alkane) and low temperature (-22 to +27 degr ees C). Catalyst turnover numbers attain 3100, the yield of oxygenated prod ucts is 22% based on the alkane. The yields of oxygenates are higher at low temperatures. The ratio of products formed (hydroperoxide : ketone : alcoh ol) depends very strongly on the conditions of the reaction and especially on the catalyst concentration (at higher catalyst concentration the ketone is predominantly produced). (C) 1999 Elsevier Science Ltd. All rights reser ved.