Chromium(III) compounds as catalysts for Hydrocarbon Oxidation and hydroperoxide decomposition

Abstract

Chromium stearate and chromium acetylacetonate are very active catalysts both for the oxidation of hydrocarbons by molecular oxygen and for the decomposition of organic hydroperoxides. During these reactions they also catalyze the oxidation of secondary alcohols to the corresponding ketones by organic hydroperoxides. From organic hydroperoxides and chromium(III)compounds chromium (VI) compounds are formed which are probably the effective agents oxidizing secondary alcohols to ketones.

Chromium-catalyzed oxidations in organic synthesis

“…Cr(acac)3-catalyzed oxidations with oxygen have also been investigated. Alkanes provided the corresponding ketones and alcohols with a ketone/alcohol ratio > l. 84 Although both epoxidation and allylic oxidation have been observed with alkenes,90,94'95'98"101 eventually in the presence of a second catalyst [Pt(PPh3)202] (Table 6),98 the selective oxidation of /9-isophorone to 3,5,5-trimethylcyclohex-2-ene-l,4-dione was achieved with the Cr(acac)3/02 system102 in good yields, when pyridine was used as solvent (eq 12).103 Note that this trans-Cr(acac)3 (0.005 equiv), neat, air, 50 °C 28.8 ref 102…”

“…Chromium esters have often been examined with the objective of obtaining catalysts soluble in organic media With this aim, a cheap fatty acid has been generally employed for the ester part, the catalyst most considered being chromium(III) stearate. 37,84,85,100,108,[117][118][119][120][121][122][123][124][125][126][127][128][129][130][131][132][133][134] The efficiency of chromium(III) acetate has been less in-vestigated37,88,106,134-141 while chromium(III) trifluoroacetate,134 chromium(III) naphthenate,108,142-145 and chromium(III) octoate146 have been rarely used.…”

“…119 The reaction of the resulting hydroperoxides has been extensively studied under similar conditions. 96,100,114,115,123,[147][148][149][150][151][152][153] In general, ketones were selectively obtained, 84,96,117,121,125,126,151,153 with lower amounts of alcohols, acids, and esters being formed. However, the presence of manganese stearate as cocatalyst has favored the formation of carboxylic acids.117,127 The activity of Cr(st)3 for cyclohexyl hydroperoxide decomposition was better than that of Cr(acac) 3.115 Following studies where the decomposition of cyclohexyl hydroperoxide by Cr(st)3 has been considered to proceed through homolytic or heterolytic pathways,84,85,115,148-151 a radical chain process has been finally accepted.…”

“…However, the presence of manganese stearate as cocatalyst has favored the formation of carboxylic acids.117,127 The activity of Cr(st)3 for cyclohexyl hydroperoxide decomposition was better than that of Cr(acac) 3.115 Following studies where the decomposition of cyclohexyl hydroperoxide by Cr(st)3 has been considered to proceed through homolytic or heterolytic pathways,84,85,115,148-151 a radical chain process has been finally accepted. 84 A ternary complex between alkane, chromium, and oxygen was envisaged as the initiator of the chain reaction leading to the oxidation of n-pentadecane. 120 Subsequently, an ESR study of valence transformations of Cr(st)3 at the initial stage of the oxidation of n-pentadecane indicated the presence of alkylchromates(VI) which decomposed heterolytically to give ketones.123 Chromium(III) stearate used in conjunction with alkyl hydroperoxides has been examined as a reagent for the oxidation at 80-125 °C of alkanes (low yields) and secondary alcohols (Tables 1 and J)).84,85 b. Cr(OAc)a…”

“…)(H20)2C1 [8/0.66/0.1] CH2C12-H20, 26 °C, Cr(salen)(H20)2C1 [8/0.66/0.1] CH2C12-H20, 26 °C, 7 h sodium hypochlorite )Cl [1/7/0.025] R4NC1, CH2C12-H20, RT, 3 h (C 24)Y 8 See section VIII for the definitions for the abbreviations and symbols. 99, (exo/endo: 32) Cr(salen)(H20)2Cl [1/0.2/0.02] H20, RT, 5 h Y/O 21 as above + /3-cyclodextrin (0.03 equiv) Y/O 40 as above + 4-methylpyridine (0.06 equiv) Y/O 44 Cr(salen)(H20)2PF6 + pyridine (0.015 equiv) [1/0.03/0.005] CH2C12, RT Y/O 82Cr(m-salen)OTf + N-pyridine oxide (0.005 equiv) [1/0.05/0.01] MeCN, 25 "C Y/O85, exo CrO(m-salen)(OTf) + JV-pyridine oxide (0-0.4 equiv) [1/0.5/0.1] MeCN, 25 "C pentafiuoroiodosylbenzene Y/O[70][71][72][73][74][75][76][77][78][79][80][81][82][83][84][85] …”