Tertiary arsine oxides

Although ethylmethylphenylphosphine oxide was the first tetrahedral phosphorus compound to be resolved only negative results were obtained when attempts were made to resolve methyl(a-naphthyl)phenylarsine oxide (142) by protonation and separation of (-I-)-a-bromocamphor-7E-sulphonate salts, or (o-carboxyphenyl)methylphenyl-arsine oxide (143) or its anhydride 144 after protonation and use of ( —)-brucine or (H-)-morphine . The reversible combination of a tertiary arsine oxide with water was recognized at the outsetand it is this property that is responsible for the racemization  

Under anhydrous conditions, however, optically active tertiary arsine oxides can be prepared from optically active tertiary arsines and dinitrogen tetraoxide. Thus, (+ )-(p-carboxyphenyl)ethylphenylarsine [( + )-36] reacts with N2O4 in nitromethane to give a solution of (-h )-(p-carboxyphenyl)ethylphenylarsine oxide [( + )-147], which lost its optical activity over 1.5 h. The optically active arsine oxides 145,146,153 were similarly generated in solution (Table 8), but only ra t emates or racemic hydrochlorides were isolated The oxides can also be prepared from the corresponding arsine sulphides 

TABLE 8. Optically active tertiary arsine oxides and sulphides 

When treated with methyl iodide, ( + )-149 in nitromethane yields the crystalline (+ )-methoxyarsonium iodide 154, which decomposes into ( —)-methyl n-butyl(p-car-boxyphenyl)arsinite (155) (equation 20) .  

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Trialkyl- and triarylarsine sulfides have been prepared by several different methods. The reaction of sulfur with a tertiary arsine, with or without a solvent, gives the sulfides in almost quantitative yields. Another method involves the reaction of hydrogen sulfide with a tertiary arsine oxide, hydroxyhahde, or dihaloarsorane. X-ray diffraction studies of triphenylarsine sulfide [3937-40-4], C gH AsS, show the arsenic to be tetrahedral the arsenic—sulfur bond is a tme double bond (137). Triphenylarsine sulfide and trimethylarsine sulfide [38859-90-4], C H AsS, form a number of coordination compounds with salts of transition elements (138,139). Both trialkyl- and triarylarsine selenides have been reported. The trialkyl compounds have been prepared by refluxing trialkylarsines with selenium powder (140). The preparation of triphenylarsine selenide [65374-39-2], C gH AsSe, from dichlorotriphenylarsorane and hydrogen selenide has been reported (141), but other workers could not dupHcate this work (140). 

Several examples have been reported of rearrangements of arsine oxides (51) to esters, initiated by alkyl halides.42 43 Reactions of tertiary arsine oxides with thiols (52) cause deoxygenation.44... 

B. From Tertiary Arsine Dihalide and Tertiary Arsine Oxides ( Arsine Oxide Method")... 

A facile method for the preparation of a variety of stabilized arsonium ylides in good yield has been developed by the action of active methylene compounds with tertiary arsine oxide or tertiary arsine dihalide. Thus triphenyl-arsine dihalides react with a number of active methylene compounds in the presence of a tertiary amine to afford arsonium ylides (6) (40). The reaction of triphenylarsine oxide with active methylene compounds in the presence of either acetic anhydride or triethylamine-phos-phorus pentoxide gave rise to arsonium ylides (6) (32, 36. 65, 67). 

Tertiary arsine oxides containing nitro groups are conveniently isolated by dissohnng the arsine in mixed acid and pouring the mixture into a large bulk of water. In this case the nitro group enters the ring in the meta position to the arsenic. 

Benzyl- or cinnamyl-triphenylarsonium bromides, upon reaction with aqueous sodium hydroxide at 100 °C, decompose into triphenylarsine oxide and toluene or 2-methyl-styrene, respectively . Since tertiary arsine oxides spontaneously racemize in water , alkaline hydrolysis of arsonium salts of this type cannot be used for the preparation of optically active arsines. 

The tetrahedral stereoehemistry of a tertiary arsine sulphide was first established in 1925, when p-earboxyphenylethylmethylarsine sulphide (7) was resolved. Unlike hygroscopic tertiary arsine oxides, arsine sulphides are air-stable non-basic eompounds with... 

M. C. A. van Vliet, 1. W. C. E. Arends, R. A. Sheldon, Tertiary arsine oxides Active and selective catalysts for epoxidation with hydrogen peroxide. Tetrahedron Lett. 40 (1999) 5239. 

The reaction of arsines with chloramine-T and related compounds gives rise to arsinimines (86,300) though these are usually isolated as the hydroxy sulfonamides (300,301,302). The hydrated compounds can also be prepared from the tertiary arsine oxide, or dihydroxide, and the appropriate amine. 

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