Csa

CHAPTER 1

Introduction Chlorosulfonic acid was first prepared by Williamson' in 1854 by the action of phosphorus pentachloride on concentrated sulfuric acid and late? by the direct action of hydrochloric acid on sulfur trioxide. Other methods of preparation include: distillation of fuming sulfuric acid (oleum) with phosphorus pentoxide in a stream of gaseous hydrogen chloride; the action of phosphorus trichloride or oxychloride, chlorine, thionyl chloride, or sulfur monochloride on concentrated or fuming sulfuric acid; passing a mixture of sulfur dioxide and chlorine into glacial acetic acid; or reaction of carbon tetrachloride with fuming sulfuric acid.3 Chlorosulfonic acid is also named chlorosulhric acid in Chemical Abstracts, but chlorosulfonic acid is the commercial name by which it is more widely known. Other names are: sulfuric chlorohydrin, sulfuric acid chlorohydrin, monochlorosulfuric acid, monochlorosulfonic acid, chlorohydrated sulfuric acid and sulfuryl hydro~ychloride.~

1 Manufacture Modern chemical plants manufacture chlorosulfonic acid by the direct union of equimolar quantities of sulfur trioxide and dry hydrogen chloride gas.4 The process is a continuous flow operation and, since it is highly exothermic, heat removal is essential to maintain the reaction temperature at 50-80 "C. The sulfur trioxide may be used in the form of 100% liquid or as a dilute gaseous mixture from a contact sulfuric acid plant. Likewise, the hydrogen chloride may be 100% gas or in a diluted form. The chemical reactor may be a packed column cooled by a water-cooled condenser to moderate the vigour of the reaction and hence avoid decomposition of the product. The chemical plant must be composed of noncorroding materials such as glass, glass-lined steel, enamel or steel coated with polytetraethylene (PTFE) so that the chlorosulfonic acid is not much contaminated with iron. A typical analysis of commercial chlorosulfonic acid would be as follows: C1SO3H 98-99.5%; H2S040.2-2%; free SO3 0-2%; HCl 0-0.5% and Fe 5-50 ppm. Chlorosulfonic acid may be stored and transported in steel containers, but in this case the iron content will be in the range 25-50 ppm. The annual production of chlorosulfonic acid increased substantially after World War 1

Chapter 1

2

I1 due to expansion of the synthetic detergent industry and of dyes, drugs and pesticides. Worldwide there are approximately twenty listed manufacturers of chlorosulfonic acid: in the USA the two major ones are EI DuPont de Nemours Co Inc (> 30 000 t yr-*) and the Gabriel Chemical Co (> 13 000 t yr-I). The price of chlorosulfonic acid has risen from approximately US$ 209 t-' in 1977 to US$ 389 t-' in 1991. Further details of the preparation of chlorosulfonic acid are given in Chapter 10, p 272.

2 Physical Properties Chlorosulfonic acid (C1SO3H) is a colourless or straw-coloured liquid which fumes in air and decomposes slightly at its boiling point. The physical properties are shown in Table 1;4 these vary slightly from sample to sample reflecting the different amounts of the various impurities present, e.g. hydrogen chloride, sulfur trioxide and related compounds. It is difficult to prepare a really pure sample of chlorosulfonic acid because of its instability at the boiling point, even under reduced pressure, which tends to degrade rather than purify the molecule. Pure chlorosulfonic acid has been obtained by fractional crystallization. Chlorosulfonic acid is a strong acid which is toxic and corrosive and behaves as a dehydrating, oxidizing and chlorinating agent. It is soluble in halocarbons containing hydrogen; for instance, chloroform, dichloromethane and 1,1,2,2-tetrachloroethanebut is only sparingly soluble in carbon tetrachloride and carbon disulfide. It is soluble in liquid sulfur dioxide, sulfuryl chloride, acetic acid, acetic anhydride, trifluoroacetic acid, trifluoroacetic anhydride and nitrobenzene.

Table 1 Physical properties of chlorosulfonic acid, ClS03H Property ~~

klue _____

Mol. wt. MP ("C) Bp ("C) at 760 mmHg Bp ("C) at 19 mm Hg Specific gravity (density), dp(g rn1-I) Viscosity, mPa.s (= cP) at 15.6 "C Viscosity, mPa.s (= cP) at 49 "C Refractive index, :n Dielectric constant at 15 "C Electrical conductivity (ohm.cm) at 25 "C Vapour density at 2 16 "C (kg m-3)(a) Heat of formation, AHf, 298, (kJ mol-I) Specific heat, kT kg-' K-' Heat of vapourization (J g-') Heat of solution in water (Hrnol-')

116.53 1 -81 to -80 151-152 74-75 1.753 3.0 1.7 1.437 6 0 f 10 0.2-0.3 X 2.4 -597.1 1.18 452-460 168.6

(a)Vapourdensity is not precise because chlorosulfonic acid partially decomposes at the boiling point

The structure of chlorosulfonic acid 1 was proved by Dharmatti' who showed by magnetic susceptibility measurements that the chlorine atom was directly

3

Introduction

attached to the sulfur atom and further supporting evidence was obtained from Raman spectral ~ t u d i e s . ~ ? ~ 0 If

CI-S-0-H II 0 1

3 Chemical Properties Chlorosulfonic acid is a powerful acid with a relatively weak sulfur-chlorine bond. It fumes in moist air producing pungent clouds of hydrogen chloride and sulfuric acid (Equation 1). CIS03H

+

H20

H2S04

+

HCI

(1)

When chlorosulfonic acid is heated it partially decomposes into sulfuryl chloride (S02C12), sulfuric acid, sulfur trioxide, pyrosulfuric acid (H2S207), hydrogen chloride, pyrosulfuryl chloride (C12S205) and other compounds. At 170 "C, there is an equilibrium between chlorosulfonic acid, sulfuryl chloride and sulfuric acid (Equation 2). Sulfur dioxide and chlorine are not observed when chlorosulfonic acid is heated between 170 and 190 "C, but do appear at higher temperatures or when it is heated in a sealed tube (Equation 3).3 170 "C

2CIS03H 2CIS03H

* SO2CI2

4

>190 "C .L

CI2

+

H2S04

+ SO2 + H2SO4

When chlorosulfonic acid is treated with powerful dehydrating agents like phosphorus pentoxide, it is converted into its anhydride, pyrosulfuryl chloride (C12S205).Chlorosulfonic acid, by boiling in the presence of mercury salts or other catalysts, decomposes quantitatively into sulfuryl chloride and sulfuric acid. It functions as a chlorinating agent with sulfur, arsenic, antimony and tin and yields sulfur dichloride and the tetrachlorides of the other element^.^ With powdered tellurium or selenium, chlorosulfonic acid gives cherry-red or mossgreen colours respectively and these can be used in spot tests for the acid. On heating with charcoal, it is decomposed with the evolution of sulfur dioxide, hydrogen chloride and carbon dioxide. In synthetic organic chemistry, chlorosulfonic acid can be used for sulfation of alcohols (Equation 4); sulfamation of amines (Equation 5); and the sulfonation and chlorosulfonation of aromatic compounds (Equations 6 and 7). In the latter reaction, there must be an excess (at least two equivalents) of the reagent present. All these reactions depend on the relative weakness of the sulfur-chlorine bond in chlorosulfonic acid. Chlorosulfonic acid only reacts slowly with saturated aliphatic hydrocarbons in the absence of a double bond or other reactive site, such as a tertiary hydrogen atom. Straight chain aliphatic alcohols, e.g. lauryl alcohol (dodecan- 1-01) can therefore be sulfated by chlorosulfonic acid without degradation or discolouration which often occurs with sulfur trioxide; this is important in the manufacture of hair shampoos,

Chapter 1

4

like sodium lauryl sulfate 2 (Equation 8); the sulfation reaction is often carried out in pyridine solution. ROH

+

+

CIS03H

ArH

+

CIS03H

+

~C12H250H+ CIS03H

+

pyridine

RNH2

ArH

* ROS03H

CIS03H

2CIS03H

* RNHS03H 4

+

[HCI]

ArS03H

+

HCI

ArS02CI

+

H2SO4

pyridine

HCI

n-C12H250S03H+ [HCI]

(6)

+

HCI

(7)

NaOH (aq.) * n-C12H25S04- Na' (8) 2

With primary or secondary amines, chlorosulfonic acid yields the corresponding sulfamic acid (Equation 5); this reaction with cyclohexylamine afforded the artificial sweetener sodium cyclamate 3 (Equation 9). In contrast to alkanes, alkenes readily react with chlorosulfonic acid to give the alkyl chlorosulfonates; thus ethylene (ethene) is absorbed by chlorosulfonic acid to give ethyl chlorosulfonate 4 (Equation 10).

3

Aromatic hydrocarbons also react smoothly with an equimolar amount of chlorosulfonic acid or an excess of the reagent to yield either the sulfonic acid or the sulfonyl chloride (Equations 6 and 7). The direct conversion of aromatic compounds into their sulfonyl chlorides (chlorosulfonation or chlorosulfonylation) is probably the most important reaction of chlorosulfonic acid because sulfonyl chlorides are intermediates in the synthesis of a wide range of sulfonyl derivatives. The process is of wide application because many substituents on the aromatic ring, e.g. alkyl, alkoxy, amide, carboxy, cyano, hydroxy, nitro and multiple bonds are unaffected by the reagent. Chlorosulfonation is essentially an electrophilic substitution reaction, consequently the reaction is facilitated by the presence of electron-donor groups, like alkyl, alkoxy and hydroxy, when it proceeds under relatively mild conditions, e.g. the minimum excess (approx. two equivalents) of the reagent, temperatures of -5 "C to 25 "C and an inert diluent such as chloroform. On the other hand, when electron-withdrawing groups, e.g. nitro, carbonyl or carboxy are present, the reaction requires more drastic conditions, e.g. a large excess of the reagent (five to ten equivalents) and heating to 100-150 oC.8 The use of chlorosulfonic acid for the synthesis of organic sulfonyl chlorides has been reviewed. The work before 1943 is described with extensive references

5

Introduction

by Suter,' by Jackson3 and, specifically for aromatic hydrocarbons, by Suter and Weston.lo More recent reviews of sulfonation were carried out by Gilbert,' Cerfontain,I2 Andersen13 and Taylor14 and of chlorosulfonation by Bassin, Cremlyn and Swinbourne.l5 The use of chlorosulfonic acid for preparation of several important arylsulfonyl chlorides has been de~cribed.'~.'~ However, depending on the nature of the substrate and the experimental conditions, reaction with chlorosulfonic acid may also yield diary1 sulfonesi8 or chlorinated products." Chlorosulfonic acid is widely used in organic qualitative analysis to prepare solid derivatives from liquid or low melting aromatic compounds, e.g. hydrocarbons, halides and ethers.'6y20The procedure involves conversion of the aromatic compound into the sulfonyl chloride, which is subsequently reacted with ammonia to yield the solid sulfonamide derivative which is suitable for melting point determination. Chlorosulfonic acid reacts with carboxylic acid anhydrides to give excellent yields of the acid chlorides2' (Equation 11). 0

4

Safety

Chlorosulfonic acid reacts explosively with water producing fumes of hydrogen chloride and sulfuric acid; the pungent vapour is toxic and highly irritating to eyes, mucous membranes, skin and the respiratory tract.22 When using the reagent, protective clothing, gloves and safety goggles are needed, because chlorosulfonic acid is highly corrosive and causes severe burns in contact with skin. Experiments using chlorosulfonic acid must be performed in an efficient fume cupboard. The acid is not itself flammable, but it can cause fires by contact with combustible materials because of the heat of r e a ~ t i o n . ~Spills .~~ should be carefully diluted with large volumes of water. Absorption onto materials, such as expanded clay, diatomaceous earth, sand or soda ash mixture is effective, especially the latter since soda ash also partially neutralizes the acid.

5 Uses Chlorosulfonic acid is employed in the manufacture of synthetic detergents such as sulfates of alkenes or unsaturated oils, polyoxypropylene glycol, long chain alcohols, alkylarenes or alkyl diphenyl ether^.^ It is also extensively used in the manufacture of sulfonamide antibacterials (sulfa drugs), diuretics and other pharmaceuticals, pesticides, artificial sweeteners (saccharin), disinfectants (chloramine and dichloramine T), plasticizers, dyes and pigments, sulfonyl polymers as plastics, and ion exchange resins. Chlorosulfonic acid is an oxidizing and

Chapter 1

6

dehydrating agent and functions as a catalyst in the esterification of aliphatic alcohols, alkylation of alkenes, and synthesis of alkyl halides from alkenic halides and isoalkanes containing tertiary hydrogen. It is used as a vulcanization accelerator, a source of anhydrous hydrogen chloride and in the tanning, textile and paper industries. Overall, the approximate breakdown of the commercial applications of chlorosulfonic acid is as follows: detergents 40%; pharmaceuticals 20%; dyes 15%; pesticides 10% and miscellaneous uses, e.g. plasticizers, ion-exchange resins, etc. 15%.

6 References 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

17 18 19 20 21 22

A.W. Williamson, Proc. R. SOC.London, 1854, 7, 11. A.W. Williamson, J: Chem. SOC.,1857, 10, 97. K.E. Jackson, Chem. Rev., 1939, 25, 83. C.E. McDonald, ‘Chlorosulfuric Acid’ in Kirk-Other, Encyclopaedia of Chemical Technology,4th Edn, Vol. 6, Wiley, New York, 1993, 168. S.S. Dharmatti, Proc. Indian Acad. Sci. Sect. A , 1941, 13, 359. R.J. Gillespie and E.A. Robinson, Can. J: Chem., 1962,40, 644. H. Gerding, J Chem. Phys., 1948, 46, 188. R.B. Wagner and H.D. Zook, Synthetic Organic Chemistry, Wiley, New York, 1965, 822. C.M. Suter, The Organic Chemistry of Sulfur, Wiley, New York, 1944. Reprinted edition by Intra-Science Research Foundation, Santa Monica, California, 1969. 1946, 3, 141. C.M. Suter and A.W. Weston, Org. React. 0, E.E. Gilbert, Sulfonation and Related Reactions, Wiley, New York, 1965. H. Cerfontain, Mechanistic Aspects in Aromatic Sulfonation and Desulfonation, Interscience, New York, 1968. K.K. Andersen, ‘Sulfonic Acid and Derivatives’ in Comprehensive Organic Chemistry, D.H.R. Barton and W. Ollis (eds), Vol. 3, Pergamon Press, Oxford, 1979, 331. R. Taylor, Electrophilic Aromatic Substitution, Wiley, Chichester, 1990, 337. J.P. Bassin, R.J. Cremlyn and F.J. Swinbourne, Phosphorus, Sulfur and Silicon, 1991, 56, 245. B.S. Furniss, A.J. Hannaford, V Rogers, P.W.G. Smith and A.R. Tatchell (eds), Vogelj. Textbook of Practical Organic Chemistry, 5th Edn, Longman, Harlow, 1989, 877, 883, 1234, 1238. R.J. Cremlyn, An Introduction to Organosulfur Chemistry, Wiley, Chichester, 1996, 100, 103, 219. A. Rieche and W. Fischer, Angew. Chem., 1957, 69,482. R.J. Cremlyn and T.N. Cronje, Phosphorus and Sulfur, 1979, 6, 459. H.T. Openshaw, Laboratory Manual of Qualitative Organic Analysis, Cambridge University Press, Cambridge, 1968, 27. L.F. Fieser and M. Fieser, Reagents for Organic Synthesis, Wiley, New York, 1967, 139. S.G. Luxon (ed), Hazards in the Chemical Laboratory, Royal Society of Chemistry, Cambridge, 1992, 302.