Antimony(V) Chloride1

SbCl5

[7647-18-9]  · Cl5Sb  · Antimony(V) Chloride  · (MW 299.02)

(Lewis acid,1 catalyst for Friedel-Crafts reactions, isomerization, and other Lewis acid related chemistry;1 chlorinating agent; acid system for the preparation of stable carbocation and onium salts1)

Alternate Name: antimony pentachloride

Physical Data: bp 92 °C/30 mmHg.

Solubility: sol chloroform, carbon tetrachloride.

Form Supplied in: colorless or slightly yellow oily liquid; commercially available.

Handling, Storage, and Precautions: SbCl5 is a corrosive, toxic, and moisture sensitive substance. It can be purified by vacuum distillation. SbCl5 fumes when exposed to atmosphere, and should be stored under anhydrous conditions and handled using proper gloves in a well ventilated hood.

Catalyst in Friedel-Crafts and Related Chemistry.

Aromatic compounds can be readily alkylated under SbCl5 catalysis.2,3 However, competing chlorination can sometimes complicate the alkylation. The activity of SbCl5 is comparable to that of Aluminum Chloride and Aluminum Bromide in the reaction of s-butyl chloride with benzene.2a It is interesting that dibenzoylchloromethane can be converted to 2-chloro-3-phenylindenone in 80% yield under SbCl5 catalysis (eq 1).3

Both acyl halides and acid anhydrides have been utilized in the acylation of arenes under SbCl5 catalysis.4,5 Reaction of 3-acetamidobenzo[b]furan with acid chlorides give condensed 1,3-oxazinium salts.4d Treatment of the salts with ammonium acetate in acetic acid gives the corresponding benzo[b]furano[3,2-d]pyrimidines in good yields (eq 2). Similar reactions proceed when 3-acetamidobenzo[b]thiophene and indole are used as substrates.4d Friedel-Crafts acylation generally requires a stoichiometric amount of Lewis acid. However, catalytic acylation can be achieved with the use of SbCl5 in conjunction with Silver(I) Perchlorate, Lithium Perchlorate, or chlorodiphenylborane.5 Trichloromethyl phenyl ketones can be readily prepared by reaction of trichlorophosphazoperchloroethane with arenes in the presence of SbCl5 followed by hydrolysis of the reaction mixtures.6

Much of the research work on SbCl5-catalyzed halogenation of arenes has focused on chlorination and bromination of perfluoroalkyl substituted aromatics.7 Iodination of arenes has also been carried out with Iodine in the presence of SbCl5.7c

Reaction of organic disulfides with electron rich aromatic compounds under SbCl5/Silver(I) Hexafluoroantimonate catalysis affords unsymmetrical aryl sulfides in modest yields.8a Electrophilic sulfinylation and sulfonation can be similarly effected by SbCl5.8b-c Alkyl- and halobenzenes give thiocyano derivatives when treated with a mixture of SbCl5 and Pb(SCN)2 in CCl4.9

Silyl enolates of a,a-dialkoxy ketones react with furans to form [3 + 2] cycloaddition products in the presence of SbCl5 (eq 3).10 Cycloaddition also occurs when 2,2-dialkoxycyclopropanecarboxylic esters and carbonyl compounds are treated with SbCl5.11

In the presence of SbCl5 and Tin(II) Trifluoromethanesulfonate, a,b-unsaturated thioesters react with silyl enol ethers to form the corresponding Michael adducts stereoselectively in high yields.12 Successive treatment of lactones with ketene silyl acetals and certain organosilane-based nucleophiles (triethylsilane, allyltrimethylsilane, trimethylsilyl cyanide, etc.) under SbCl5/Me3SiCl/SnI2 catalysis affords a-mono- or a,a-disub-stituted cyclic ethers (e.g. eq 4).13

Catalyst in Isomerization and Rearrangements.

Along with many other Lewis acids, SbCl5 has been applied to promote the Fries rearrangement.14 More recently it has been found that the SbCl5/AgSbF6 system is an efficient catalyst for Beckmann and pinacol rearrangements.15 In the presence of SbCl5, (E)-2-methoxy-2,4-diphenyl-3-butenenitrile can be isomerized to the corresponding g-methoxy-a,b-unsaturated carbonitriles in good yield.16 Methyl 6a-chloropenicillanate rearranges to (3S)-6-chloro-2,3,4,7-tetrahydro-2,2-dimethyl-7-oxo-1,4-thiazepine-3-carboxylate when treated with SbCl5 in CH2Cl2. Under similar conditions, methyl penicillanate and methyl 6b-phthalimidopenicillanate undergo analogous isomerizations (eq 5).17

Halogenation.

In addition to its ability as a halogenation catalyst, SbCl5 itself is an excellent chlorinating agent and has been widely applied to chlorination of various organic compounds, including arenes, alkenes, and alkynes.18-24

Preparation of Carbocation and Onium Ion Complexes.

SbCl5 has been extensively utilized in the preparation of stable carbocations and onium ions.25-30 This is facilitated by the ready formation of the stable anion SbCl6-. The carbocations generated include such stable ions as halophenylcarbenium ions, cyclopropenyl cations, and perchloroallyl cations.26 Extensive studies have also been carried out on the use of SbCl5 to synthesize onium salts such as alkylidene ammonium salts, 2-azaallenium salts, nitrilium salts,27 oxonium salts,28 and sulfonium salts.29 Reaction of adamantylideneadamantane with SbCl5 gives the stable chloronium [AdAdCl+][SbCl6-] salt.30

Other Reactions.

1,3-Dithianes can be converted to the corresponding carbonyl compounds in excellent yields in the presence of SbCl5.31 When epoxides are treated with a catalytic amount of SbCl5/AgSbF6 in the presence of alkoxytrimethylsilane and triethylsilane, sequential reactions involving rearrangement and reductive condensation give the corresponding ethers in good yields (eq 6).32 Homologation of ketones with diazoacetic esters can also be catalyzed by SbCl5 (eq 7).33


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George A. Olah, G. K. Surya Prakash, Qi Wang & Xing-ya Li

University of Southern California, Los Angeles, CA, USA.



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