Alkyl sulfates hydrolysis

Although hydrolysis of alkyl sulfates by sulfatases is noted in Part 1 of this chapter, ether cleavage has been shown to be the major pathway for the degradation of dodecyltriethoxy sulfate (Hales et al. 1986). 

The acid hydrolysis of micellized alkyl sulfates (Kurz, 1962 Motsavage and Kostenbauder, 1963) has recently been very carefully reinvestigated (Garnett et al., 1983). For relatively dilute micellized alkyl sulfate, salt inhibition follows the predictions of the pseudophase ion-exchange model, with the expected salt order. But this order is not followed with more concentrated alkyl sulfate, and these results are a very interesting deviation from the widely observed pattern of micellar salt effects. 

Alternatively one could suggest that a micellized sulfuric or sulfonic acid is not strong. For example, apparent acid dissociation constants of weak acids decrease when the acids are bound to anionic micelles (Hartley, 1948), and the rapid hydrolysis of micellized alkyl sulfates at low pH is consistent with... 

Another possibility of transforming indirectly alcohols into alkyllithium compounds consists in nsing the corresponding sulfates. Alkyl sulfates 60 were lithiated using naphthalene (4%) as the electron carrier catalyst in THF at —78 °C yielding two equivalents of the corresponding alkyllithinm 61. Further addition of an electrophile at —78 to 0°C led to the formation, after hydrolysis, of the final prodncts 20 (Scheme 22) ... 

The head groups of these surfactant molecules are negatively charged. The most widely used anionic surfactants are those containing carboxylate groups, such as soaps, sulfonate, and sulfate ions Soaps, which are salts of weak carboxylic acids, are formed by the hydrolysis of fats (triglycerides) by sodium hydroxide. Sulfonates, such as sodium docusate and decane sulfonate, have been widel used in pharmaceutical systems. The most popular alkyl sulfate is sodium lauryl sulfate, which is... 

On the other hand, the acid-catalyzed hydrolysis of alkyl sulfates may proceed by a mechanism analogous to equation 18 or by equilibrium protonation followed by rate-determining attack of water on sulfur ... 

The effect of increasing the hydrocarbon chain length from methyl to octadecyl on the acid catalyzed, neutral, and base catalyzed hydrolysis of n-alkyl sulfate esters has been examined (Kurz, 1962). The rate constants for the neutral hydrolysis decrease smoothly from methyl to dodecyl sulfate and hence are unaffected by micellization of the longer chain esters. The rate constants for the acid-catalyzed hydrolysis, however, are relatively constant for the non-micellar ester but increase dramatically with micelle formation (Table 7). Conversely, the hydroxide... 

The activation parameters for the acid-catalyzed hydrolysis of long chain alkyl sulfates compared to those for non-micellar ethyl sulfate calculated from potentiometric data indicate that the rate acceleration accompanying micellization is primarily a consequence of a decrease in the enthalpy of activation rather than an increase in the entropy (Kurz, 1962). However, the activation energies for the acid-catalyzed hydrolysis of sodium dodecyl sulfate calculated from spectrophotometric data have been reported to be identical (Table 8) for micellar and non-micellar solutions, but the entropy of activation for the hydrolysis of the micellar sulfate was found to be 6 9 e.u. greater than that for the non-micellar system (Motsavage and Kostenbauder, 1963). This apparent discrepancy may be due to the choice of the non-micellar state as the basis of comparison, i.e. ethyl sulfate and non-micellar dodecyl sulfate, to temperature dependent errors in the values of the acid catalyzed rate constant determined potentiometrically, or to deviations in the rate constants from the Arrhenius equation. 

Olefinic acyl halides, hydrolysis, 418 preparation, 547, 549 preparations listed in table 61, 551 Olefinic alcohols, alkylation by alkyl sulfates, 229 dehydration, 33, 42 isomerization, to aldehydes, 296 to ketones, 349... 

Fio. 5. Aoid-catalyzed hydrolysis rate of sodium alkyl sulfates as a function of the number of carbon atoms (n) in the alkyl chain 0.04 M sodium alkyl sulfate, temp. 90° ionic strength—excluding contribution of micelles—0.04, —O— 0.46,-- ------. 

The effect of the chain length of sodium alkyl sulfates on the acid-catalyzed hydrolysis of methyl orthobenzoate (65) is illustrated in Fig. 6. It can be seen that up to a given concentration there seems to be... 

Water is likely to be present in aU practically relevant catalytic applications unless extreme precautions are taken or the system is self-drying (e.g., due to the fact that strong Lewis-acids or metal alkyls are used as co-catalysts). Water will influence the ionic liquid s thermal stability significantly if any part of the ionic liquid is prone to hydrolysis. Apart from the weU-known hydrolysis lability of tetrafluoroborates and hexafluorophosphates, water will thus also affect the stability of ester functionalities in the ionic liquid, e.g. the stability of alkyl sulfate anions. The presence of Bronsted acidity in the reaction system will further promote this kind of thermally induced hydrolysis reaction. Additionally, in strong Lewis-acidic ionic liquids care has to be taken to avoid incompatibilities between oxygen and nitrogen functionalities in the reactants or impurities and the ionic liquid s Lewis acidic group (usually a complex anion). It is for example obvious that the Pd-catalyzed dimerization of methylacrylate caimot be carried out in acidic chloroaluminate ionic hquids since the ionic liquid s anion would decompose in an irreversible reaction with the substrate methylacrylate. 

Sodium alkyl sulfates are esters. Thus sodium dodecyl sulfate is sensitive towards hydrolysis, especially in acid solutions. In this case, the starting fatty alcohol and sodium hydrogen sulfate is formed. Hydrolysis, once started, will run autocatalytically because the sodium hydrogen sulfate formed in this reaction is an acid in itself. Alkyl sulfates are stable in storage when in their highly pure states. 

By tradition, surfactants are stable species. Among the surfactant work-horses, e.g. anionics such as alkylben-zene sulfonates and alkyl sulfates, nonionics such as alcohol ethoxylates and alkylphenol ethoxylates, and cationics such as alkyl quats and dialkyl quats, only the alkyl sulfates are not chemically stable under normal conditions. Through the years the susceptibility of alkyl sulfates to acid-catalysed hydrolysis has been seen as a considerable problem, particularly well-known for the... 

In aqueous solution, the effectiveness of micellar systems as catalysts is quite often found to increase with the length of the alkyl chain. For example, the rate of acid hydrolysis of methyl o-benzoate in the presence of sodium alkyl sulfates increases in the order Cs < Cio < Cn < Cu < Cie. Such a result may be attributed to either electrostatic or solubilizing effects, or both. It might be expected that any effects due to electrostatic interactions would also increase. Alternatively (or additionally), the increasing aggregation number found in the series may result in a significant increase in the solubilizing power of the system. The importance of each mechanism will depend upon the specifics of the reaction. 

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