Transacylation reactions derivatives

Catalysts for Transacylation Reactions of Carboxylic and Phosphoric Acid Derivatives... 

Poly(methyl 3-(l-oxypyridinyl)siloxane) was synthesized and shown to have catalytic activity in transacylation reactions of carboxylic and phosphoric acid derivatives. 3-(Methyldichlorosilyl)pyridine (1) was made by metallation of 3-bromopyridine with n-BuLi followed by reaction with excess MeSiCl3. 1 was hydrolyzed in aqueous ammonia to give hydroxyl terminated poly(methyl 3-pyridinylsiloxane) (2) which was end-blocked to polymer 3 with (Me3Si)2NH and Me3SiCl. Polymer 3 was N-oxidized with m-ClC6H4C03H to give 4. Species 1-4 were characterized by IR and H NMR spectra. MS of 1 and thermal analysis (DSC and TGA) of 2-4 are discussed. 3-(Trimethylsilyl)-pyridine 1-oxide (6), l,3-dimethyl-l,3-bis-3-(l-oxypyridinyl) disiloxane (7) and 4 were effective catalysts for conversion of benzoyl chloride to benzoic anhydride in CH2Cl2/aqueous NaHCC>3 suspensions and for hydrolysis of diphenyl phosphorochloridate in aqueous NaHCC>3. The latter had a ti/2 of less than 10 min at 23°C. 

Catalysis in Transacylation Reactions. The principal objective of the study was to evaluate 4 as an effective organic soluble lipophilic catalyst for transacylation reactions of carboxylic and phosphoric acid derivatives in aqueous and two-phase aqueous-organic solvent media. Indeed 4 catalyzes the conversion of benzoyl chloride to benzoic anhydride in well-stirred suspensions of CH2CI2 and 1.0 M aqueous NaHCC>3 (Equations 1-3). The results are summarized in Table 1 where yields of isolated acid, anhydride and recovered acid chloride are reported. The reaction is believed to involve formation of the poly(benzoyloxypyridinium) ion intermediate (5) in the organic phase (Equation 1) and 5 then quickly reacts with bicarbonate ion and/or hydroxide ion at the interphase to form benzoate ion (Equation 2 and 3). Apparently most of the benzoate ion is trapped by additional 5 in the organic layer or at the interphase to produce benzoic anhydride (Equation 4), an example of normal phase-... 

Bobowsky and Shavel found an interesting intramolecular reductive transacylation reaction, in which substituted cyclopent[e][l,3]oxazin-2-ones and l,3-perhydrobenzoxazin-2-ones (90) were formed (80JHC277). In the reactions of 4-(2 -oxocycloalkyl)-3,4-dihydro-3-methyl-2//-l,3-benzoxazin-2-ones 88 and potassium borohydride, the 2 -hydroxycycloalkyl products 89 obtained underwent intramolecular transacylation reactions, resulting in the dihydro-1,3-oxazine derivatives 90. In this way, the 4-(2 -oxocycloalkyl)... 

Transacylation is the transfer of the acyl group from one G group to another, resulting in the formation of various acid derivatives. Figure 16-1 summarizes the transacylation reactions. Notice that the more reactive derivatives are convertible to the less reactive ones. Because acetic anhydride reacts less violently, it is used instead of the more reactive acetyl chloride to make derivatives of acetic acid. In aqueous acid, the four kinds of carboxylic acid derivatives in the figure are hydrolyzed to RCOOH in base, to RCOO". 

Sulfonic acids, R(Ar)S03H, form derivatives similar to those of carboxylic acids (see Table 16-3). These are sulfonyl chlorides, sulfonates (esters), and sulfonamides. The transsulfonylation reactions are similar to the transacylation reactions, except that the ester and amide cannot be made directly from the acid. See Problem 13.17 for preparation of sulfonyl chlorides and esters and Problem 13.18 for use of sulfonate esters as substrates in S l and S,42 reactions. 

The results of these studies and others reported previously demonstrate that the 1-oxypyridinyl group is an effective catalyst for the transacylation reactions of derivatives of carboxylic and phosphoric acids when incorporated in small molecules and polymers. Furthermore, this catalytic site exhibits high selectivity for acid chlorides in the presence of acid anhydrides, amides, and esters. Therefore, catalysts bearing this group as the catalytic site can be used successfully in synthetic applications that require such specificity. The results of this work suggest that functionalized polysiloxanes should be excellent candidates as catalysts for a wide variety of chemical reactions, because they combine the unique collection of chemical, physical, and dynamic-mechanical properties of siloxanes with the chemical properties of the functional group. Finally, functionalized siloxanes appear to mimic effectively enzyme-lipophilic substrate associations that contribute to the widely acknowledged selectivity and efficiency observed in enzymic catalysis. 

Reactions using other derivatives of carboxylic acids 3.2.4.23 Rearrangement and transacylation reactions... 

The present discussion was intended to analyze molecular recognition in substrate binding. Of course molecular recognition also plays a major role in molecular catalysis and transport processes where transformation or translocation of the bound substrates is brought about by a suitably functionalized receptor molecule. These most important aspects are however beyond the scope of this presentation. One may just note, for the sake of illustration, that for instance cysteinyl derivatives of receptor (12 b) display marked chiral recognition in transacylation reactions with optically active substrates [26] and that dicarboxylate-dicarboxamide analogs of (12 b) allow pH regulation of the Ca /K selectivity in competitive transport of calcium and potassium ions [27]. Further information about the results obtained in the areas of molecular catalysis and transport may be found respectively in the references [28] and [29] and in the references cited therein. 

The feasibility of bonding pyridinyl groups to silicon which contains a hydrolytically sensitive functional group has recently been demonstrated 15-71. 2-Fluoro-3-(dimethylchlorosilyl)pyridine and 3-fluoro-4-(dimethylchloiosilyl)pyridine as well as 2-, 3-, and 4-(dimethylchlorosilyl)pyridine were prepared by the reaction of the corresponding lithiopyridines with excess Me2SiCl2- Hydrolysis of the pyridinyl substituted chlorosilanes gave disiloxanes which were insoluble in water. In the present report we will describe extension of this work to include pyridinyl dichlorosilanes which can be hydrolyzed to polysiloxanes. These polymers can be N-oxidized and the resultant derivatives have been shown to be effective hydrophobic transacylation catalysts. 

With HNOj, polynitration would occur since NMc2 is very activating. NO is less electrophilic than NO2. REACTIONS WITH CARBOXYUC ACID DERIVATIVES , TRANSACYLATIONS... 

REACTIONS WITH CARBOXYLIC ACID DERIVATIVES TRANSACYLATIONS... 

Similar reactions involving polymer amide anions yield the corresponding diacylamine structures along with substituted /3-oxoamides, keto amides (XIII) and (XIV). In this way, the sequence of condensation and transacylation results in the formation of five types of 3-keto acid derivatives (X)—(XIV). 

Reactions with Carboxylic Acid Derivatives Transacylations... 

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