Sulphonic acid catalysts

We have cited the case of epoxidation with peracids earlier in this book. A cross-linked polymethacrylic acid can, in principle, be treated with a sulphonic acid catalyst and H2O2 to give the peracid, which will allow epoxidation to be carried out in a convenient way, while the polymer can be reused. The key advantage is that the product stream does not contain an acid, which may be harmful in several ways. 

The reaction proceeds as given below using sulphonic acid catalyst and a reaction temperature below 140°C commensurate with residence time and speed of reaction ... 

A wide diversity of catalysts have been supported on polymers [14, 17, 18, 19], but perhaps the four most important groups are asymmetric catalysts, phase transfer catalysts, sulphonic acid catalysts and transition metal complex catalysts. 

The sample, for example, polyethylene glycol, is reacted with acetic anhydride in the presence of toluene-p-sulphonic acid catalyst to produce a glycol diacetate ... 

Cases are also known where a reaction product is firmly held to catalytic sites and diffuses out at a prohibitively low rate. The effect has been observed in several cases, including the esterification of alcohols, acting as reactant and solvent [16, 20]. It is thought that in these reactions water is the product which poisons the acidic sites of the sulphonic acid catalyst. A more straightforward case is the hydrolysis of amides where one of the reaction products, the amine, forms an ammonium salt with the resin acid and thus decreases the number of free acid groups [21]. Similarly, cationic reaction products (formed from cationic reactants) may be retained in the resin by virtue of its ion exchanger function. 

Maki-Arvela (1999) has developed a new polyolefin supported sulphonic acid catalyst for esterification of acetic acid with methanol. The esterification kinetics (pseudo-homogeneous) was modeled with a mechanistic rate equation, the parameters of which were determined by non-linear regression. The esterification rate constant of the most active modification of the new catalyst was 9.6 x 10 ° dm /(mol g min) at 328 K, which clearly exceeds the corresponding value obtained with a traditional (Amberlyst 15) polyvinyl benzene supported catalyst, 1.5 x 10 ° dm /(moP g min). 

A number of basic materials such as hydroxides, hydrides and amides of alkaline and alkaline earth metals and metal oxides such as zinc oxide and antimony oxide are useful catalysts for the reaction. Acid ester-exchange catalysts such as boric acid, p-toluene sulphonic acid and zinc chloride are less... 

The effect of the catalyst-steroid ratio has been studied for the p-toluene-sulphonic acid-catalyzed ketalization of androst-4-ene-3,17-dione. Selective formation of the 3-monoketal is observed with the use of an equimolar amount of ethylene glycol and a low ratio of catalyst to steroid. ... 

Tertiary amine N-oxides may also be used to convert sulphoxides to sulphones16. The reaction proceeds by initial attack by the N-oxide oxygen atom on the sulphoxide moiety, followed by subsequent elimination of the amine. In order to obtain good yields, the reaction must be carried out at 190°Cfor 20 hours with a 20-fold excess of N-oxide in the presence of acid catalysts. The sulphone must then be separated by chromatography, thus making the method less attractive than other procedures and so it has not been employed synthetically. 

The availability of Nafion on silica has not only lowered the cost of the resin but also has made it versatile (Sun et al., 1997 Harmer et al., 1998). A number of industrially important reactions have been attempted, with considerable success, with these catalysts. Consider the Fries rearrangement of phenyl acetate to p-acetyl phenol (/t-hydroxy acetophenone). This has been accomplished by Hoelderich and co-workers (Heidekum, 1998). In the ca.se of alkylation of benzene with benzyl alcohol, Amberlyst-15 and p-toluene sulphonic acid are ineffective and Nafion on silica works well at 80 °C. 

Gonzalez and Holt (1981) have shown how macrocyclic lactones can be made conveniently in microemulsion media. Thus, intramolecular e.sterification of (o-hydroxy alkanoic acids can be carried out with a very small amount of acid catalysts like p-toluene sulphonic acid, and rates are markedly higher as compared to simple media. 

The water formed in the reaction is continuously removed from the reaction mixture by azeotropic distillation, in order to avoid reversible reaction between water and ester. The progress of reaction can be followed either by measuring the amount of water or by determining the amount of unreacted acid in aliquots withdrawn at regular intervals of time. The reaction can be carried out either in presence of a catalyst, i.e. a weak acid like p-toluene sulphonic acid (a strong acid can hydrolyse the polymer, formed) or in absence of the catalyst. 

Ahmed Kabir etal. (1992) treated wood with DMDHEU as well as DMDHEU combined with a vinyl polymer, and determined the dimensional stability of the wood. Methane sulphonic acid was used as a catalyst in both cases. DMDHEU treatment resulted in a 50 % reduction in radial swelling following immersion in water for 100 minutes, with the combined treatment being snperior. However, the ASE (one cycle) of DMDHEU treated wood (30%) was snperior to that fonnd for the combined treatment (17%). DMDHEU appeared to be stable to hydrolysis over a number of wetting cycles. When DMDHEU-treated samples were exposed in ontdoor weathering trials, they exhibited considerable variation in moistnre content and developed severe surface checks, whereas the combined treatment showed snperior performance. 

In similar fashion a diaminodisaccharide derivative( 7P) has been prepared from the appropriate oxazoline and 6-ol in nitromethane using toluene- -sulphonic acid as catalyst 49). 

Aryl glycosides of 2-amino-2-deoxy sugars, as might be expected, can be prepared by similar techniques as was illustrated by the synthesis of phenyl 3,4,6-tri-0-acetyl-2-acetamido-2-deoxy-p-D-glucoside and -D-galactoside by toluene -sulphonic acid catalysed reactions between phenol and the hexosamine penta-acetates These products were then anomerised using zinc chloride as catalyst to provide means of obtaining -anomers. 

CH3CH(OBu-n)2 - Acetaldehyde is the carbonyl component, butanol the nucleophile, and toluene sulphonic acid is the catalyst. How would you hydrolyse PhCH(OEt)a, and what would you get ... 

Catalyst Ion exchanger with DVB content (%) p-toluene- sulphonic acid... 

Thus, in theory, a limited quantity of sulphuric acid can convert an unlimited quantity of alcohol to ether, but in practice, owing to side reactions, this does not hold. Sulphuric acid may be replaced by phosphoric, arsenic, or benzene-sulphonic acid. By using a mixture of alcohols mixed ethers may be obtained. Simple ethers are formed simultaneously, however. For mixed ethers it is better to use the methods given on pp. 216, 217. As a catalyst in the above reaction, sand or aluminium sulphate may be employed. The method is applicable to naphthols, but not to phenols. 

Tetrahydropyranyl ethers, THP-ethers, are formed by reaction of an alcohol with 2,3-dihydropyran in the presence of an acid catalyst. The procedures below illustrate the use of concentrated hydrochloric acid or pyridinium toluene-p-sulphonate. Amberlyst H-15 resin has also been used as a reaction catalyst.81... 

A recent procedure for the preparation of methyl esters involves refluxing the carboxylic acid with methanol and 2,2-dimethoxypropane in the presence of toluene-p-sulphonic acid as the catalyst (Expt 5.146). The water produced in the esterification process is effectively removed by acid-catalysed reaction with the ketal to give acetone and methanol. 

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