Organic Syntheses, Coll. Vol. 6, p.1028 (1988); Vol. 51, p.4 (1971).
A 5-l., three-necked flask
fitted with a mechanical stirrer
, a thermometer
, and a dropping funnel
equipped with a calcium chloride drying tube
is charged with 112.2 g. (1.002 mole) of freshly distilled 2,4,4-trimethyl-1-pentene (Note 1)
and 1 l. of dichloromethane (Note 2)
. The flask is immersed in an ice–salt bath
, and the stirred solution is cooled to 0–5°. A solution of 158 g. (1.02 moles) (Note 3) of freshly distilled chromyl chloride (Note 4)
in 200 ml. of dichloromethane (Note 5)
is added dropwise with stirring from the dropping funnel while the temperature is maintained at 0–5° (Note 6)
. The reaction mixture is stirred for 15 minutes, and 184 g. of 90–95% technical grade zinc dust (Note 7)
is added. The mixture is stirred for 5 minutes, 1 l. of ice water and 400 g. of ice are added as rapidly as possible (Note 8)
, and the mixture is stirred for an additional 15 minutes. The ice–salt bath is replaced with a heating mantle
, and the flask is fitted for steam distillation. After distillation of the dichloromethane
the residue is steam distilled (Note 9)
. The distillate is transferred to a separatory funnel
, the organic layer is separated, and the aqueous layer is washed with three 50-ml. portions of dichloromethane
. The combined organic phases are distilled (Note 10)
through a 56-cm., vacuum-jacketed, Vigreux column
, removing the solvent. The product is transferred to a 250-ml. round-bottomed flask
and distilled. After removal of a small amount of dichloromethane
the fraction boiling at 45–52° (15 mm.)
is collected, giving 90–100 g.
) (Note 11)
The alkene is available from Aldrich Chemical Company, Inc., or Phillips Petroleum Company, and can be used without distillation.
The material available from Matheson, Coleman and Bell or Eastman Organic Chemicals is satisfactory except as explained in (Note 5)
The fraction, b.p. 115.5–116.5°
, is used. Chromyl chloride is available from Alfa Inorganics, Inc.
The time required for the addition is about 60 minutes.
This approximate fivefold excess is necessary to reduce the higher valence chromium salts, thereby eliminating overoxidation and double bond cleavage. The zinc dust used was obtained from Allied Chemical Corporation
The temperature usually increases to 8–10°.
It is not necessary to dry the organic phase.
The checkers, working at two-thirds scale, obtained the product in 70–71%
has been prepared by the catalytic isomerization of 1,2-epoxy-2,4,4-trimethylpentane
in both the liquid and gas phases (77–92%
and by the oxidation of 2,4,4-trimethyl-1-pentene
with chromium trioxide in acetic anhydride
Although the catalytic isomerization of the epoxide2
in good yield, this requires epoxidation of the alkene as the first step. The chromyl acetate
and chromic acid
oxidative methods give unsatisfactory yields.3
In the preparation described here, 2,4,4-trimethylpentanal
is obtained from the alkene in good yield, in one step. Also, this preparation illustrates a general and convenient procedure for the direct oxidation of 2,2-disubstituted-1-alkenes (Table I) to unstable and reactive aldehydes.4
The reaction is very fast and the aldehyde is the major product.
In contrast to the relative simplicity of the chromyl chloride
oxidation of 2,2-disubstituted-1-alkenes to aldehydes, the chromyl acetate
and chromic acid
oxidations generally lead to epoxides, acids, and carbon–carbon double bond cleavage. For example, chromyl acetate
primarily to 1,2-epoxy-4,4-dimethyl-2-neopentylpentane
in low yield,9
and chromic acid
oxidizes the alkene principally to 4,4-dimethyl-2-neopentylpentanoic acid
Chemical Abstracts Nomenclature (Collective Index Number);
acetic anhydride (108-24-7)
chromic acid (7738-94-5)
chromium trioxide (1333-82-0)
Pentanal, 2,4,4-trimethyl- (17414-46-9)
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