Organic Syntheses, CV 4, 910
Submitted by R. L. Shriner and Calvin N. Wolf
1.
Checked by Cliff S. Hamilton and Yao-Hua Wu.
1. Procedure
Caution! All steps in the following preparations should be performed under a hood, since volatile arsenic compounds may be liberated.
A.
Triphenylarsine. In a
2-l. round-bottomed three-necked flask is placed
130 g. (5.65 g. atoms) of powdered sodium2 covered with
900 ml. of benzene. The flask is fitted with an
Allihn condenser, a
mercury-sealed mechanical Hershberg stirrer, and a
500-ml. dropping funnel in which is placed a mixture of
170 g. (0.94 mole) of arsenic trichloride and
272 g. (2.42 moles) of chlorobenzene. About
10 ml. of the arsenic trichloride-chlorobenzene mixture is dropped into the flask, and the reaction mixture is stirred and heated on a
steam bath until it darkens and boils spontaneously. The steam bath is removed, and the remainder of the
arsenic trichloride-chlorobenzene mixture is added dropwise, with stirring, over a period of 1–1.5 hours at such a rate that gentle boiling is maintained (Note
1). When the addition is complete, the mixture is stirred and heated under reflux on a steam bath for 12 hours.
The reaction mixture is filtered while hot through a
large Büchner funnel, and the filtrate is collected in a
3-l. filter flask. The residue (Note
2) is washed on the funnel with two
200-ml. portions of hot benzene, pressed as dry as possible, and then transferred to a
1-l. beaker, boiled with
300 ml. of benzene, and filtered, the same funnel and flask being used. This extraction process is repeated twice.
The combined
benzene filtrates are subjected to distillation from a steam bath to remove the
benzene. The flask containing the residual red oil is connected to a
water pump and heated under reduced pressure in an
oil bath at 110–120° for 2 hours to remove unreacted starting materials. When cooled, the crude
triphenylarsine solidifies to a light brown solid which melts at
57–59°. The yield is
230–240 g. (
93–97%). The crude product is dissolved in
650–700 ml. of hot 95% ethanol and placed in a
refrigerator overnight. The crystals are collected on a Büchner funnel and washed with
50 ml. of cold 95% ethanol. The yield is
218–225 g. (
88–91%) of white crystals which melt at
61°.
B.
Triphenylarsine oxide. In a
500-ml. round-bottomed flask equipped with a mechanical stirrer, a
thermometer, and a
100-ml. dropping funnel is placed
100 g. (0.33 mole) of the recrystallized triphenylarsine (Note
3) dissolved in
200 ml. of acetone. To the solution
46 g. (0.41 mole) of 30% hydrogen peroxide is added dropwise, with stirring, over a period of 20–30 minutes. A
water-ice bath is used to maintain the temperature at 25–30°. When the addition is complete, stirring is continued for 30 minutes, and the
acetone is then removed by distillation.
The flask containing the residual yellow oil is fitted with a
water trap and condenser, and
120 ml. of benzene is added. The water is then removed by azeotropic distillation (Note
4). When the removal of water is complete, the
triphenylarsine oxide is crystallized by cooling the flask in an
ice bath for 1.5–2 hours. The light-brown crystals are collected on a Büchner funnel and washed on the funnel with
25 ml. of cold benzene. The crude product weighs
97–98.5 g. (
91–93%) and melts at
186–188°. The crude product is transferred to a
porcelain dish and triturated with
50 ml. of benzene, collected on a Büchner funnel, pressed as dry as possible, and washed with
25 ml. of cold benzene. After drying in the air, the
triphenylarsine oxide amounts to
89–92 g. (
84–87%) of white crystals, melting at
189°.
C.
Tetraphenylarsonium chloride hydrochloride. In a 2-l. round-bottomed three-necked flask fitted with a condenser, a mercury-sealed mechanical Hershberg stirrer, and a dropping funnel is placed
40 g. (0.124 mole) of triphenylarsine oxide dissolved in
1 l. of hot benzene. To this solution there is added with vigorous stirring a solution of
phenylmagnesium bromide which is prepared from
34.6 g. (0.22 mole) of bromobenzene,
6.0 g. (0.25 g. atom) of magnesium, and
200 ml. of dry ether. A brown viscous solid separates. The mixture is stirred for 15 minutes and then stirred and heated under reflux on a steam bath for 30 minutes. The solvent is removed by decantation, and the viscous solid is washed with
500 ml. of benzene. The addition product is then hydrolyzed with 100 ml. of water containing
5 ml. of concentrated hydrochloric acid.
The hydrolysis mixture is transferred to a
1-l. round-bottomed flask fitted with a
reflux condenser, and
500 ml. of concentrated hydrochloric acid is added (Note
5). The mixture is heated on a steam bath for 1.5–2 hours. The flask is cooled in an ice bath; the crystals are collected on a
sintered-glass funnel and washed with
200 ml. of ice-cold concentrated hydrochloric acid and then with
200 ml. of ice-cold dry ether. The crude product weighs
50–56 g. The product is dissolved in a mixture of 50 ml. of water and
150 ml. of concentrated hydrochloric acid by boiling under reflux. The
tetraphenylarsonium chloride hydrochloride separates when the solution is cooled in an ice bath. The white needles are collected on a sintered-glass funnel and washed with
50 ml. of ice-cold concentrated hydrochloric acid and then with
200 ml. of ice-cold dry ether. The yield of
tetraphenylarsonium chloride hydrochloride melting at
204–208° with decomposition is
42–45 g. (
74–80%).
2. Notes
1. If the addition of the
arsenic trichloride-chlorobenzene mixture is too rapid, the reaction becomes vigorous and must be moderated with a cooling bath.
2. Before being discarded, the residue should be treated with
ethanol to destroy unreacted
sodium.
3. If crude
triphenylarsine is used, the final product is difficult to purify
4.
Triphenylarsine oxide is partly converted to the dihydroxide when heated with water. However, it is not hygroscopic under ordinary conditions.
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3. Discussion
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