[7790-94-5] · ClHO3S · Chlorosulfonic Acid · (MW 116.53)
(strong acid with weak sulfur-chlorine bond; a strong sulfating, sulfonating, and dehydrating agent; also a chlorinating agent)
Alternate Name: chlorosulfuric acid.
Physical Data: mp -81 to -80 °C; bp 151-152 °C/755 mmHg; d 1.753 g cm-3.
Solubility: sol 1,1,2,2-tetrachloroethylene, chloroform, dichloromethane, nitrobenzene, acetic acid, and acetic anhydride; slightly sol carbon disulfide and carbon tetrachloride; reacts with alcoholic solvents.
Form Supplied in: colorless liquid.
Handling, Storage, and Precautions: strong acid, causing severe chemical burns if in contact with skin; use in a fume hood, since fumes are hazardous and extremely irritating to eyes, nose, and respiratory tract; reacts violently with moisture, releasing HCl and H2SO4; store under nitrogen in a cool dry place.
Aromatic compounds react with chlorosulfonic acid to produce the corresponding sulfonated products.2 The resulting sulfonic acids react with excess chlorosulfonic acid to produce sulfonyl chlorides (eqs 1 and 2).
This method has been used to prepare the sulfonated derivatives of benzene,2 benzoic acid,3 acetanilide,4 naphthalene,2 and anthracene.5 Additional examples include chlorosulfonation of biphenyl (eq 3),6 chlorophenols,6,7 benzophenone,8 diphenyl sulfone,8 and ferrocene.9
Arylsulfonamides are obtained by the reaction of aromatic compounds with ClSO3H followed by ammonia (eqs 4 and 5).10
Treatment of aromatic amino acids such as tyrosine and tryptophan with ClSO3H leads to the formation of the corresponding arylsulfonic acids (eq 6). This technique has been used to modify peptides.11
Some abnormal products are obtained when aromatic halides react with ClSO3H. For example, p-dichlorobenzene and p-dibromobenzene undergo chlorination on reaction with ClSO3H in the presence of iodine (eq 7).2a,12 Fluorobenzene, iodobenzene, o-dichlorobenzene, and o-dibromobenzene yield the corresponding sulfones.2a,12
Chlorosulfonic acid has been used to prepare a-sulfonated derivatives of carboxylic acids (eqs 8 and 9).13
Treatment of alcohols with ClSO3H produces the corresponding sulfate esters. By this method the carotenoid alcohols lycoxanthin and zeaxanthin were converted to their sulfate esters (eqs 10 and 11).14 The hydroxy amino acids serine and threonine are converted to their corresponding sulfate esters by ClSO3H.11 Carbohydrates15 and chitin16 are also sulfated by treatment with ClSO3H.
Reaction of amines with ClSO3H produces sulfamates (eq 12).17
ClSO3H has been used to chlorinate polycyclic alkanes such as adamantane (eq 13).18,19
Aliphatic acids react with ClSO3H in the presence of chlorine to give corresponding a-chloro acids (eqs 14 and 15).20
Chlorosulfonic acid catalyzes the rearrangement of 1,2,4-trioxalans (ozonides) to 1,2,4,5-tetraoxans (eq 16).21
Cyclopropenyl carboxylic acids and esters have been efficiently decarbonylated using ClSO3H and this method has been used for the generation of cyclopropenyl carbocations (eqs 17 and 18).22
Treatment of benzils with excess of ClSO3H leads to the formation of chlorosulfonated phenylbenzofurans (eq 19).23
Prabu C. Prabhakaran
Bristol-Myers Squibb, New Brunswick, NJ, USA