Acylium perchlorate

Cationic Polymerization. The functional groups that enable initiation of cationic polymerization can be introduced on the inorganic surface. The introductions of acylium perchlorate Reaction (5), sulfonium or pyridinium salt, or active chloride... 

Acylation of 3-acetonyl-5-alkylthieno[2,3-fe]thiophenes 208 and 3-acetonyl-5-methylthieno[3,2-fe]thiophenes (209) in a mixture of aliphatic acid anhydride and perchloric acid (actually, acylium perchlorate) was demonstrated (79KGS1424) to occur at the free a position followed by cyclization and formation of perchlorates of tricyclic pyrylium salts 210 and 211 (yields > 80%). The latter are transformed into thieno[2, 3 5,4]- (212) and -[2, 3 4,5]thieno[2,3-c]pyridmes 213 in yields higher than 90% by passing ammonia through their suspensions. 

Praill, having discovered the efficiency of acylium perchlorates as acylating agents, decided to examine the esterification of /err-butanol as opposed to its dehydration to isobutene. Using acetic anhydride and perchloric acid mixtures, both tert-h xty acetate and isobutene were rapidly produced and in accordance with the known alkyl oxygen fission of tertiary esters, the proportion of isobutene increased with time. In these reactions where acetic anhydride was in excess, crystalline material was deposited in the mixture. Later this was shown to be 2,4,6-trimethylpyrylium perchlorate, identified by its conversion to 2,4,6-trimethyl pyridine and its picrate. When isobutene itself was acylated using acetic anhydride and perchloric... 

Cationic Ring-opening Polymerization and Copolymerization of Oxepane Initiated by Acylium Perchlorate Groups on Carbon Black. Journal of Polymer Science, Polymer Chemistry Edition, 26, 2715-2724... 

These reactions are presumed to occur through aroyl triflate intermediates which dissociate to aiyl acylium ions. Lithium perchlorate and scandium triflate also promote acylation. ... 

Not only water and alcohols, but also other oxygen compounds, are able to react covalently with acylium ions. In the case of hydroxy compounds the product is stabilized by loss of the proton from the hydroxyl group, but certain ethers give an analogous reaction in which the product is stabilized by loss of a carbonium ion.288 Using acetyl chloride with silver perchlorate in nitromethane as the source of acetyl... 

In contrast to this demonstration of bimolecularity, Hall and Lueck82 showed the possibility of acylium ion formation from benzoyl chloride by its reaction with mercuric perchlorate. In common with dimethylcarbamyl chloride, dimethylsulphamyl and tetramethyldiamidophosphochloridate, benzoyl chloride reacted readily to form the corresponding acylium ion /i-butyl chloroformate however was inert. Kivinen138 studied the effect of mercuric chloride on the ethanolysis of 4-methoxybenzoyl chloride, benzoyl chloride and 4-nitrobenzoyl chloride and obtained the following approximate relative rates for the effect of mercuric chloride (0.30 M) in ethanol, 4-MeO, 2.91 4-H, 1.00 4-NOz, 1.03, confirming the SN2 character of the 4-nitro-... 

It should be noted that the alkyl aryl ketones 191 react with the mixture of perchloric acid and acetic anhydride under the same conditions (room temperature, 10-20 h) to give the unsymmetrical pyrylium salts 197114,115. As shown in Reference 112 this reaction is also an example of electrophilic catalysis by acylium ions, proceeding via the cationic intermediates 195 and 196 (equation 62). 

The same authors116 showed that 1,3-diketones 198 react easily with benzonitrile in the presence of a HC104-Ac20 mixture to form 3-azapyrylium perchlorates 199 (equation 63). This reaction did not occur without acetic anhydride, which is a catalyst since the acylium ions are not included in the end products. The application of the C-acylated ketones 198 leads to 3-azapyrylium salts 199 which are isomeric to those mentioned above (194), i.e. products 199 have an inverted orientation of heteroatoms comparatively to the three-carbon fragment of the cycle116. The azapyrylium salts 199 can be hydrolyzed to the enamides 200. 

Solutions of carboxylic acids or anhydrides in strong mineral acids also give rise to the protonation of the weaker component, but often the reaction goes further and leads to the formation of acylium ions. Thus, in the case of acetic acid dissolved in such strong acids as sulphuric, perchloric and trifluoromethanesulphonic acids, dehydration of the protonated species (ACOH2) gives the corresponding acetyl ester and/or its ionised form. The same endproduct is obtained if acetic anhydride is used instead of its acid ... 

Acidic catalysts such as toluene -sulphonic or perchloric acids are known [13] to afford the reactive acylium ions (as ion pairs) in acid aidiydrides ... 

A number of protic acids have been used to catalyze acylation reactions. It is assumed that the reactions involve the generation of acylium ions. Polymeric reagents such as Nafion-H have been used for example 2-fluorobenzoyl chloride and toluene give the benzophenone derivatives with an ortho.para ratio of 4 81. ° A zeolite-catalyzed acylation (equation 6) has been reported to afford 4-dodecenoyltol-uene in 96% yield but the yields are low with short chain carboxylic acids. Early examples of the use of trifluoroacetic and perchloric acids reported good yields of products. Some more recent examples are shown in equations (7) to (9). Phosphoric and polyphosphoric acids have been used together with carboxylic acids (equation 10),anhydrides and acylureas (equation 11). °... 

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