Chromic Acid Oxidation of 2-Propanol

Step 1 Reaction of the alcohol with chromic acid gives an alkyl chromate. 

Step 2 The oxidation step can be viewed as a p elimination. Water acts as a base to remove a proton from carbon while the O—Cr bond breaks. 

Step 3 A series of redox reactions converts chromium from the 4+ oxidation state in HCr03 to the 3+ oxidation state. 

Typical conditions involve formation of the chlorodimethylsulfonium ion in dichlo-romethane at low temperature, followed by addition of the alcohol to be oxidized, then treatment with a weak base such as triethylamine. Primary alcohols yield aldehydes secondary alcohols yield ketones. 

Mechanism 15.4 outlines the mechanism, starting with reaction of the alcohol with chlorodimethylsulfonium ion (steps 1-2). Steps 3-4 describe what happens after the amine base is added. 

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Sodium Borohydride Reduction of an Aldehyde or Ketone 653 Acid-Catalyzed Formation of Diethyl Ether from Ethyl Alcohol 660 Chromic Acid Oxidation of 2-Propanol 665... 

Mechanism 15.3 outlines the mechanism of chromic acid oxidation of 2-propanol to acetone. The alcohol reacts with chromic acid in the first step to give a chromate ester. A carbon-oxygen double bond is formed in the second step when loss of a proton from carbon accompanies cleavage of the bond between oxygen and chromium. The second step is rate-determining as evidenced by the fact that (CH3)2CHOH reacts 6.7 times faster than (CH3)2CDOH. If the second step were faster than the first, no deuterium isotope effect (Section 5.17) would have been observed. 

Recently Mosher and Driscoll 2 have noted that the polymerization of acrylonitrile can be observed during the chromic acid oxidation of 2,2-dimethyl-l-phenyl-l-propanol. The polymerization is caused by radicals formed during the oxidation of benzaldehyde (which is one of the cleavage product of phenyl-1-butylcarbinol). The oxidation of benzaldehyde is due to the chromium(IV), most probably, or chromiun(V) intermediates. 

Suitable mechanisms have been proposed following determination of the kinetic and activation parameters for oxidation of 2-naphthol and cyclic ketones by nicotinium dichromate some a-amino acids by tripropylammonium fluorochromate " distyryl ketone by quinaldinium fluorochromate methanol by benzyltriethylammonium chlorochromate catalysed by 1,10-phenanthroline substituted benzyl alcohols by tetraethylammonium bromochromate L-cysteine by pyridinium bromochromate lactic acid and 3,5-dimethyl-2,6-diaryl piperidin-4-one oximes by pyridinium chlorochromate allyl alcohol by IDC benzophenoxime by bispyridine silver(I) dichromate and alkyl phenyl sulfides by cetyltrimethylammonium dichromate. A non-linear Hammett plot obtained for the oxidation of substituted benzyl alcohols by IDC has been attributed to the operation of substituent effect on two steps of the proposed mechanism. " Kinetic and activation parameters for oxidation of o-toluidine and of A-methyl-2,6-diphenyl piperidin-4-one oxime and its 3-alkyl derivatives by sodium dichromate have been determined and suitable mechanisms have been suggested. Micellar catalysis in the 1,10-phenanthroline-promoted chromic acid oxidation of propanol... 

Exercise 15-28 In the conversion of 2-propanol to 2-propanone with chromic acid, which is the redox step, esterification or elimination What is the change in oxidation level of carbon in this reaction ... 

The Cr /l-propanol, Cr /l,2-propane diol, Cr /phenyl tert-h xXy alcohol, Cr /thiourea, and Cr /ethylene thiourea systems have been studied in the polymerization of acrylonitrile [194,195]. These studies furnished information on polymerization kinetics and the general mechanism of chromic acid oxidations. The mechanism involves the formation of unstable species such as and Cr ". ... 

Trimethylacetic acid may be made by the hydrolysis of tert-butyl cyanide with weak hydrochloric acid at ioo0.1 It is also obtained by oxidation of trimethylpyroracemic acid with silver oxide or potassium dichromate and sulfuric acid,2 by oxidation of tertf-butylethylene with permanganate solution,3 or by oxidation of dimethyl 2,2-propanol with chromic acid.4 Schroeter reports the formation of trimethylacetic acid by rearrangement of the oxime of trimethylacetophenone to give the anilide of trimethylacetic acid, which can be hydrolyzed to give the acid.5... 

Oxidation of isopropyl alcohol (H2R) by chromic acid has been studied in det ai by Westheimer and Novick , and it was found that acetone (R) is formed nearly quantitatively. The reaction proved to be first order with respect to hydrogen chromate and second order with respect to hydrogen ions. Measurements using 2-deutero-2-propanol under identical conditions as those for the oxidation of ordinary isopropyl alcohol showed the rate of reaction to be of that with the hydrogen compound. This fact is considered to prove that the secondary hydrogen atom is removed in the rate-controlling step and that the assumption of hydride-ion abstraction can be excluded. The data are consistent with the following mechanism... 

The oxidation of the primary hydroxyl groups in 3-phenyl-2-lV-acetylamino propanol and propargylic alcohol by electrogenerated chromic acid has been reported. jV-Acetylphenylalanin and propargylic acid are both formed in 90% current yield. 

It was claimed by Henry(Ref 2) that 0. de Battice prepd nitroacetone in 1895 in Belgium by oxidation of nitroisopropanol with chromic mixture. Henry described the compd as a coi, mobile liq with a sharp odor, a 1.070 at 14°, bp 152° at 767 mm and insol in w. Lucas c]aimed(Ref 3) that the compd described by Henry was not nitroacetone, but this statement was disputed by Henry(Ref 4). Harries also claimed(Ref 5) that the compd described by Henry is not nitroacetone More recently, Hass Hudgin(Ref 7) claimed that they had isolated some nitroacetone from the high-boiling fraction of the vapor-phase nitration of acetone but it is not clear from their paper whether the substance was liq or solid. Hurd NilsonfRef 8) prepd nitroacetone as pale-green crysts, mp 47°, by oxidizing 1—nitro—2—propanol with sodium dichromate and sulfuric acid. The yield was (5% of theoretical. The explosifcility of this compd was not mentioned... 

The ester is given as having a molecular formula of CeHiaOa, which indicates each R (R ) is made of 2 carbons. Since chromic acid only oxidizes primary alcohols, the alcohol portion of the ester must be from propanol (CH3CH2CH2OH). This leaves only the acid propionic... 

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