Acidolysis mechanism

Mass spectrometry is an analytical method of choice for identification of volatile compounds and has been employed in investigation of thermolysis and acidolysis mechanisms of chemical amplification resists [96, 121, 122]. This technique has been also utilized in screening of resists systems, especially Si-containing 193 nm bilayer resists,for outgassing [438,439]. MALDI-TOF mass spectroscopy has been applied to characterization of dendritic resist polymers. 

Pos twe-Tone Photoresists. The ester, carbonate, and ketal acidolysis reactions which form the basis of most positive tone CA resists are thought to proceed under specific acid catalysis (62). In this mechanism, illustrated in Figure 22 for the hydrolysis of tert-huty acetate (type A l) (63), the first step involves a rapid equihbrium where the proton is transferred between the photogenerated acid and the acid-labile protecting group ... 

In a series of organic acids of similar type, not much tendency exists for one acid to be more reactive than another. For example, in the replacement of stearic acid in methyl stearate by acetic acid, the equilibrium constant is 1.0. However, acidolysis in formic acid is usually much faster than in acetic acid, due to higher acidity and better ionizing properties of the former (115). Branched-chain acids, and some aromatic acids, especially stericaHy hindered acids such as ortho-substituted benzoic acids, would be expected to be less active in replacing other acids. Mixtures of esters are obtained when acidolysis is carried out without forcing the replacement to completion by removing one of the products. The acidolysis equilibrium and mechanism are discussed in detail in Reference 115. 

In view of the proposed mechanism for this cleavage reaction, it was reasonable to expect that certain allylic ethers for which an elimination pathway existed (Scheme II) would also be susceptible to cleavage under thermolysis, acidolysis or a combination of both. 

FIGURE 3.5 Deprotection of functional groups by acidolysis.5 Protonation followed by car-bocation formation during the removal of benzyl-based protectors by hydrogen bromide. Two mechanisms are involved in generating benzyl bromide from the protonated substrates. 

FIGURE 3.6 Deprotection of functional groups by acidolysis. Protonation followed by carbocation formation during the removal of ferf-butyl-based protectors by hydrogen chloride.8 One mechanism is involved in generating the ferf-butyl cation, which is the precursor of two other molecules. 

FIGURE 6.27 Acidolysis removes a protector by one or both of the depicted mechanisms. Pg = protector, Y = residue, Nu = nucleophile. Nu1 and Nu2 may be identical or different. C02 is liberated when Pg = alkoxycarbonyl. 

A range of mechanisms is possible for the acidolysis of phosphorus amides, depending on the nucleophilicity of the departing amine. A recent study of phosphinic amides (160) in acidic media demonstrated that, when R2 is aryl, the presence of an o-Me group reduced the hydrolysis rate significantly, and also that the mechanism appears to be of an associative type.128 The phosphinic halides (161 X = Cl or F R = Me) are more reactive, probably for steric reasons, than the corresponding halides (161 R = Bu1) in 5 n2(P) solvolyses with aqueous acetone and with alkali. In the case of the t-butyl compounds, the fluoride is more reactive to OH- than is the chloride.129... 

Davies and Roberts7 have shown that the dibutyl ester of optically active 1-phenylethylboronic acid is cleaved by C7H15C02D in boiling diglyme to yield (—)-l-deuterioethylbenzene with 95 % retention of configuration. The acidolysis was suggested7 to proceed by mechanism SE2(cyclic), reaction (4),... 

Abraham and Hill22 suggested that the mechanism of acidolysis was that of SE2(cyclic), in which electrophilic attack at the carbon atom undergoing substitution was an important feature the reactivity sequence p-toluidine > cyclo-hexylamine is that of acid strength. A transition state such as (IV) is thus indicated. 

Jensen and Rickborn60 have severely criticised the work of Dessy on the acidolysis of dialkylmercurys by hydrogen chloride. They state that, in their view, no firm mechanistic conclusions can be drawn from the published results , although a four-centred mechanism at present seems to be reasonable. 

Assuming that acidolysis proceeds only by mechanism SE2 (see text). b Cis-trans ratio unknown. 

Many electrophilic reagents are capable not only of electrophilic attack at the carbon atom of the C-M bond, but also of nucleophilic attack at the metal atom of the C-M bond. It is such nucleophilic attack that gives rise to the mechanisms SE2(cyclic) and SE2(co-ord). Dessy et al.12,13 have several times stressed the importance of internal nucleophilic assistance by the electrophilic reagent in reaction mechanisms of organometallic compounds, and it is the account by Dessy and coworkers13 of the acidolysis of triethylboron that is probably the classic report in this field. 

In solvent diglyme, the rate of acidolysis of triethylboron by carboxylic acids is found to be greater the weaker is the acid, there being a linear correlation between log k2 and the pK of the carboxylic acid. Thus nucleophilic coordination of the carboxylic acid to the boron atom must be an important feature of the reaction mechanism, and the acidolysis may therefore be denoted as following mechanism SE2(cyclic) or SE2(co-ord), perhaps through a transition state such as (I). ... 

It is generally agreed that both processes, namely addition polymerization (the nature of active species still of much debate) and acidolysis/ condensation reaction, occur simultaneously in the cationic ring-opening polymerization [247,248], although the contribution of both mechanisms is still a matter of discussion. Kinetics of the acid-catalyzed condensation of silanol groups was studied in detail [249,250]. 

TFA at higher temperatures,or TFA/thioanisole where the push-pull mechanism remarkably increases the rate of acidolysis,f l liquid HF/pyridine,t °l BBrj/CHaQa, or BBrj/TFA for longer peptide fragments.By these procedures also the benzyl-type side-chain protection is cleaved as well as Arg(Tos). Additionally, numerous sulfonic acids were shown to efficiently remove the Z group, such as methanesulfonic acid, trifluoromethanesulfonic acid, or fluorosulfonic acid mainly in CH2CI2 or Since the acidolytic removal of the... 

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