Sulphonated methyl esters

As a class of surfactant, sulphonated methyl esters (SMEs) have been known since the 1980s, but have not been widely commercialised. Through the late 1990s into 2000, there were signs of increased use in Asia and the United States across a variety of applications. They share many similarities with olefin sulphonates but, importantly, they are made from renewable oleochemical feedstocks. This is preferred by many formulators, particularly in cosmetic and personal care applications. 

As esters, SMEs can be hydrolysed under certain conditions. In the pH range 5-9, SMEs are very stable, even at temperatures close to their boiling points but, as pH moves outside the optimum, hydrolysis rates increase. In the great majority of personal care and household formulations, hydrolysis is not an issue. 

Products are normally supplied as a 30-40% solution, although products with a high level of sulphofatty acid will be viscous pastes at these concentrations, so secondary surfactants are often blended into such products to improve their storage and handling properties. 

SMEs can also be dried and their powder properties are better than LAS, making SME an attractive ingredient in laundry powders. Products containing high sulphonated fatty acid as the disodium salt also have good solid forms and are used in personal care applications as ingredients in bar products. 

Raw materials. The hydrophobe for SME is currently derived exclusively from oleochemical sources, rather than from petrochemicals, as in the case of LAS and AOS. While these two sources can often provide surfactants of equivalent performance, oleochemcials are frequently preferred (especially in personal care applications) because they are derived from natural ingredients. The use of renewable resources is also cited as an additional benefit of oleochemical-based surfactants and this is discussed more fully in Section 4.2.1. 

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Distilled fatty methyl esters with low iodine values are used as the starting raw material for the production of SME. The fatty methyl ester is first reacted with sulfur trioxide at 80-90°C in a falling-film reactor. The dark product obtained from this process is bleached using hydrogen peroxide. After bleaching, the lighter color product is neutralized with alkali to produce an a-sulphonated methyl ester. 

Base-induced elimination of sulphinate from homoallylic sulphones , from y-ketosulphones , and from 1,2-bissulphones has been used in synthetic sequences ranging from the preparation of retinoic acid and of its methyl ester , to a novel pentannulation sequence that leads to a range of cross-conjugated dienes , as exemplified by equation (69). The overall yield for the two steps was 63%. 

Solid esters are easily crystallisable materials. It is important to note that esters of alcohols must be recrystallised either from non-hydroxylic solvents (e.g. toluene) or from the alcohol from which the ester is derived. Thus methyl esters should be crystallised from methanol or methanol/toluene, but not from ethanol, n-butanol or other alcohols, in order to avoid alcohol exchange and contamination of the ester with a second ester. Useful solvents for crystallisation are the corresponding alcohols or aqueous alcohols, toluene, toluene/petroleum ether, and chloroform (ethanol-free)/toluene. Carboxylic acid esters derived from phenols are more difficult to hydrolyse and exchange, hence any alcoholic solvent can be used freely. Sulphonic acid esters of phenols are even more resistant to hydrolysis they can safely be crystallised not only from the above solvents but also from acetic acid, aqueous acetic acid or boiling n-butanol. 

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. 

Carbon-13 n.m.r. spectroscopy has been used to study benzylisoquinoline and tetrahydroisoquinoline alkaloids and their JV-methyl quaternary salts.30 N-Benzylpapaverinium bromide has been shown to undergo aerial oxidation in alkaline solution to 2-benzyl-6,7-dimethoxyisoquinolone and to give bases of general structure (10) with methylamine, benzylamine, and pyrrolidine.31 Chlorosulphonation of papaverinol affords the sulphonic acid ester (11), mild hydrolysis of which yields the acid (12), which with diazomethane is esterified and dehydrated to (13).32 N-Methyl-l,2-dihydropapaverine has been shown by kinetic studies and orbital-symmetry requirements to rearrange to the salt (14) by the route previously postulated.33... 

Other organic compounds that have been determined in sewage effluents include the following (see Table 15.13) hydrocarbons, alcohols, carboxylic acids, esters, chlorobenzenes, nitrosamines, ethylene diamine tetraacetic acid, nitriloacetic acid, organophosphorus compounds, linear alkyl benzene sulphonates, methyl mercaptan, polychlorobiphenyls and chlorinated insecticides. 

Chemistry and general properties. The product is prepared by reacting a fatty acid, typically oleic acid (a 08 1 acid), with oleum, or preferably sulphur trioxide. If a saturated fatty acid is used, the product is an a-sulphofatty acid, R(S03H)C00H and the reaction mechanism is thought to be similar to that previously suggested for the sulphonation of methyl esters. With the use of an unsaturated acid, such as oleic, the picture becomes more complex. The reaction chemistry is not fully understood, but the product is a mixture of y-hydroxy sulpho fatty acid and o -sulphonated oleic acid. 

Raw materials. It is possible to use any fatty acid as a feed material for sulphonation but economic considerations dictate that oleochemical material be preferred. Fatty acids are readily obtained from vegetable and animal oils and fats which are fatty acid triglycerides. These are transesterified to generate glycerol and three moles of a fatty acid ester, normally a methyl ester. The methyl ester can be distilled to give a specific cut and the fatty acid finally isolated by hydrolysis or hydrogenation of the ester. It is common to use animal fats (tallow) in which case the dominant C chains are 16 and 18. 

Horie, K. (2004) New process of methyl ester sulphonate and its application. Proceedings 6th World... 

METHYL ESTER STEARIC ACID see MJWOOO METHYL ESTER of WOOD ROSIN see MFT500 METHYL ESTER of WOOD ROSIN, partially hydrogenated (FCC) see MFT500 METHYLE (SULFATE de) (FRENCH) see DUDIOO 4,4 - (1 -METHYL-1,2-ETHANEDIYL)BIS-2,6-PIPERAZINEDIONE see PIK250 METHYL ETHrVNE SULFONATE see MJW250 METHYL ETHANE SULPHONATE see MJW250... 

Esters, Carboxylic Acids, and Ethers.—The rates of hydrolysis of 3(3- and 6(3-acetoxy-4 ,5 -epoxides and 1 a-acetoxy-2(3,3 (3-epoxides were observed to be accelerated relative to those acetates not containing a neighbouring epoxide group.24 Bile acid methyl esters were readily prepared from the carboxylic acids by reaction with methanol in the presence of toluene-p-sulphonic acid.25 Bile acids were readily converted into the amino-amides (14) by successive reaction with Bu N-... 

The latter was converted via the alcohol, toluene-p-sulphonate, and nitrile to homodaphniphyllic acid. Its methyl ester (164) was subsequently found as a natural product. ... 

In contrast to the usual reaction of aromatic aldehydes with cyclic ketones o-nitrobenzaldehyde condenses with 17-ketones to produce good yields of seco-acids, a reaction which has been applied to the preparation of 16-oxa-steroids. Thus, 3 -hydroxy-5a-androstan-17-one or its acetate affords the seco-steroid (153), which can be oxidised either as the free acid by ozone and alkaline hydrogen peroxide to the diacid (155) or, as its methyl ester (154), with chromium trioxide to the monomethyl ester (156). Diborane reduction of the diacid (155) or lithium aluminium hydride reduction of the dimethyl ester (157) gave the trans-diol (158), cyclised with toluene-p-sulphonic acid to 16-oxa-androstan-3)5-ol (159) or, by oxidation with Jones reagent to the lactone (152) (as 3-ketone) in quantitative yield. This lactone could also be obtained by lithium borohydride reduction of the monomethyl ester (156), whilst diborane reduction of (156) and cyclisation of the resulting (151) afforded the isomeric lactone (150). The diacid (155) reacted with acetic anhydride to afford exclusively the cis-anhydride (161) which was reduced directly with lithium aluminium hydride to the cis-lactone (160) or, as its derived dimethyl ester (162) to the cis-diol (163) which cyclised to 16-oxa-14)5-androstan-3) -ol (164). 

Virtually all of the methods for determining acyl groups developed up to now are based on re-esterification of the initial compound with sulphuric acid, a mixture of methanol with hydrochloric or p-toluenesulphonic acid, or with a mixture of p-toluene-sulphonic acid and its methyl ester [165—170]. The esters formed in the reaction were determined by analysing an aliquot of the reaction solution or by blowing-off the reactor with a carrier gas. Alkaline hydrolysis with subsequent determination of acetic acid has also been used for identifying acyl groups [167]. 

Sulphonic acids/sulphonates have been determined via conversion to the corresponding sulphonyl chlorides, then reacting these with methanol to yield the methyl esters these were determined by GLC164 or HPLC165 (see Section II.C.3 below). 

The sulphonates derived from fatty acid alkyl esters (mainly, as sodium salts of a-sulphomonocarboxylic esters or, in other words, methyl ester sulphonates) become more and more attractive in view of their renewable raw material sources, such as triglycerides of animal and vegetable origin. Fatty acid alkyl esters are produced via a direct transesterification of triglycerides with alcohol, typically methanol, or via direct esterification of fatty acids. The same thin-film sulphonation techniques (see Table 1.5) with gaseous SO3 are used today to manufacture these surfactants [62, 70]. The two-step sulphonation can be represented by the sequential reactions [70, 71] shown in Fig. 1.4. 

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