Organic Syntheses, CV 5, 969
Submitted by Ted J. Logan
1
Checked by William E. Parham and John R. Potoski.
1. Procedure
Into a
250-ml. round-bottomed flask equipped with a
magnetic stirrer and
reflux condenser fitted with a
drying tube containing Drierite® are placed
150 ml. of dimethoxyethane (Note
1),
27.8 g. (0.15 mole) of sodium trichloroacetate (Note
2), and
31.3 g. (0.1 mole) of phenylmercuric chloride. The stirred mixture (Note
3) is heated to reflux (

85°) by use of a heating mantle.
Carbon dioxide evolution, which begins shortly after heating is begun. is accompanied by the appearance of a precipitate of
sodium chloride. The reactants are heated at the reflux temperature until no more
carbon dioxide evolution is obvious (

1 hour), then cooled to room temperature and poured into 500 ml. of water. The resulting mixture, consisting of a dense oil layer, a solid, and an aqueous layer, is extracted with four
50-ml. portions of diethyl ether. The combined
ether layers are then washed with two 50-ml. portions of water, dried over anhydrous
magnesium sulfate, filtered, and the solvent removed using a
rotary evaporator. The resulting white solid, which weighs
44.8 g., is dissolved in
130 ml. of hot chloroform and fractionally crystallized. The first three fractions weigh
2.3 g. and are recovered phenylmercuric chloride. Successive reduction of solvent volume and further fractional crystallization provides
25.6 g. of product (
65% yield), m.p.
110° (Note
4) and (Note
5).
2. Notes
1. The
1,2-dimethoxyethane (monoglyme) was purchased from Matheson Coleman and Bell and purified by distillation from
lithium aluminum hydride. The use of unpurified solvent had little effect on the yield of product.
2.
Sodium trichloroacetate may be purchased from the Dow Chemical Company (96.4% pure by Cl analysis) or prepared by neutralizing
trichloroacetic acid (Matheson Coleman and Bell) with aqueous
sodium hydroxide to the
phenolphthalein end point. The product is dried under vacuum for 12 hours, sieved, then dried an additional 12 hours under vacuum, all at room temperature. The salt prepared by this method and used in this preparation was 98.5% pure, based on chlorine analysis, and can be stored indefinitely without decomposition. The submitter has obtained nearly identical yields of
phenyltrichloromethylmercury from the commercial and from the prepared salts.
3. If all the reactants are stirred for several minutes at room temperature, they dissolve to give a turbid solution. Stirring while heating then becomes unnecessary, except to promote more even heating, since the refluxing solvent and
carbon dioxide evolution keep the precipitated
sodium chloride in suspension.
4. Purity of the product was ascertained by quantitative X-ray fluorescence analysis for
chlorine and
mercury, which showed satisfactory agreement with calculated values. Compounds containing both
mercury and
chlorine are difficult to analyze by classical "wet" analytical procedures.
5. Yields as high as
77% have been obtained by this procedure. It is difficult to recover all the product from the mother liquor. The use of a
1:1 ratio of sodium trichloroacetate and phenylmercuric chloride gave yields of
39–45%, while a 1.25:1 ratio gave a
61% yield of product.
3. Discussion
This procedure is essentially identical with that previously published by the submitter.
2
4. Merits of the Preparation
Phenyl(trihalomethyl)mercurials, including the title compound, can be thermally decomposed in the presence of olefins to yield the corresponding dichlorocyclopropane derivatives.
2,9,10,11 Olefins such as
tetrachloroethylene and
ethylene, which give exceptionally low yields of dichlorocyclopropanes when treated with other reagents for generating dichlorocarbene (:CCl
2), give reasonable yields of dichlorocyclopropanes when heated with phenyltrichloromethylmercurials.
12
These mercurials have also been employed in the preparation of dihalomethyl derivatives of
carbon,
silicon, and
germanium,
13 in the conversion of carboxylic acids to dichloromethyl esters,
14 in the deoxygenation of
pyridine N-oxide,
5 in the synthesis of diarylcyclopropenones from diaryl acetylenes,
15 and in numerous other applications. Leading references to these applications may be found in a recent review on the use of phenyl (trihalomethyl)mercury compounds as divalent carbon transfer reagents.
16
This preparation is referenced from:
1718
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