Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Dealkylation esters

Alkyl bromides. Alcohols are converted into bromides by reaction with bromotrimethylsilane (1.5-4 equiv.) in CHCI3 at 25-50° (equation I). The reaction occurs with inversion. Tertiary and benzylic alcohols react more rapidly than primary or secondary alcohols. Bromides are not formed under the same conditions from Irimethylsilyl ethers of alcohols. However, trimethyl orthoformate is converted into methyl formate, HC(OCH3)3 —s HCOOCH3. Unlike iodotrimethylsUane, the bromosilane does not dealkylate esters, ethers, or carbamates. [Pg.343]

There have been further applications of MesSil and MesSiBr as dealkylating agents for ethers, esters, phosphonic acid esters, and alcohols, the last reaction using McsSil being a useful alkyl iodide synthesis. MesSil also converts acetals into ketones or sulphoxides into sulphides, whilst a mixture of PhSiMes and I2 is capable of dealkylating esters at ca. 110°C. ... [Pg.189]

Cytochrome P450 enzymes are the most widespread, active, and most versatile in their xenobiotic Phase I transformation activity. These enzymes are composed of heme-containing enzymes in the ferric ion state. In transformations the ferric ion is reduced to the ferrous ion that can bind Oj and CO. These enzymes basically add oxygen or remove hydrogen in a step-wise process to generate Phase I biotransformation products. Most cytochrome P450 transformations require an additional enzyme (co-enzyme) to assist in the transfer of electrons. Cytochrome P-450 enzymes carry out many kinds of oxidations - hydroxylations, epoxidations, heteroatom oxidations, N-hydroxylations, dealkylations, ester hydrolysis, and dehydrogenation. [Pg.350]

Alkyl esters are efficiently dealkylated to trimethylsilyl esters with high concentrations of iodotrimethylsilane either in chloroform or sulfolane solutions at 25-80° or without solvent at 100-110°.Hydrolysis of the trimethylsilyl esters serves to release the carboxylic acid. Amines may be recovered from O-methyl, O-ethyl, and O-benzyl carbamates after reaction with iodotrimethylsilane in chloroform or sulfolane at 50—60° and subsequent methanolysis. The conversion of dimethyl, diethyl, and ethylene acetals and ketals to the parent aldehydes and ketones under aprotic conditions has been accomplished with this reagent. The reactions of alcohols (or the corresponding trimethylsilyl ethers) and aldehydes with iodotrimethylsilane give alkyl iodides and a-iodosilyl ethers,respectively. lodomethyl methyl ether is obtained from cleavage of dimethoxymethane with iodotrimethylsilane. [Pg.21]

Fluoromethyl)phosphonate ester anions react with CO2 or COS to yield esters of the type (161 Y=0 or S) which may be dealkylated to the free acid through the use of bromotrimethyl-silane, but the course of the reaction with CS2 depends on the individual ester thus, (162) yields (163), but (165) is formed from (164). 22... [Pg.170]

We next investigated the dealkylation of S-b-tBM with TMSI. Unlike the reaction with S-b-MM, it required only 4 hr at room temperature to completely cleave the t-butyl ester. Work-up under acidic conditions gave S-b-MA which was virtually identical by NMR, IR, GPC, and titration with that just described above. Likewise, neutralization with KOH resulted in quantitative conversion to S-b-MA.K. Although the initially formed product of the reaction of alkyl esters with TMSI is presumably the trimethylsilyl ester (1 7 ), we were not able to isolate or characterize this copolymer. It is known that trimethysilyl methacrylate and its polymers spontaneously hydrolyze even in moist air (19). Any traces of water in the methanol used to precipitate the reaction mixture would thus preclude isolation of the intermediate trimethylsislyl ester. [Pg.288]

Additionally, they observed a second pathway, hydrolysis through dealkylation leading to a secondary ester of phosphoric acid which still contains the p-nitrophenyl moiety, i.e., de-ethyl Parathion (O-clhyl-O-p-nilrophenyl-monothiophosphoric acid) ... [Pg.424]

Warren, S. and Williams, M.R., Electrophilic substitution at phosphorus dealkylation and decarboxylation of phosphinylformate esters, Chem. Com-mun., 180, 1969. [Pg.98]

By analogy to N- and O-dealkylation reactions, one might expect esters and amides to be susceptible to P450-catalyzed oxidative attack at the a-carbon to oxygen (esters) or a to nitrogen (amides). This is indeed the case and was first established (132) by demonstration that the pyridine diester (Fig. 4.66) was oxidatively cleaved by rat-liver microsomes to yield the monoacid as shown. [Pg.85]

FIGURE 4.66 P450-catalyzed oxidative O-dealkylation of an ester. [Pg.85]

Dry hydrogen halide was passed into the ester. The ethyl halide was trapped at — 78°, and the weight of it served to indicate the progress of dealkylation. Dealkylation being completed, volatile matter was removed from the residue at low pressure. Crude acids were thus obtained in absence of water. Similar results to those obtained at 100° were obtained at 25°, but of course longer reaction time was required. [Pg.122]

Metabolism Glucuronidation N-demethylation Ester hydrolysis to morphine Glucuronidation demethylation (CYP2D6) Ester hydrolysis N-demethylation N-Dealkylation, then hydroxylation N-Demethylation Plasma and tissue esterases... [Pg.226]

Phenylcarbamates, or carbanilates, generally exhibit low water solubilities, and thus they are almost immobile in soil systems. Chlorpropham and Propham are readily volatilized from soil systems, but Terbutol and Carbaryl (Fig. 10, Table 3) are not. Ester- and amide-hydrolysis, N-dealkylation and hydroxylation are among the chemical reactions that carbamates undergo. The N-methylcar-bamate insecticides (Fig. 10, Table 3) commonly used in soils are Carbaryl, Methiocarb,Aldicarb,and Carbofuran [74,173]. [Pg.31]

As in carboxylic esters it is possible to substitute alkoxy groups of Fischer-type carbene complexes by non-carbon nucleophiles, such as other alcohols [73,214,218], enols [219], aliphatic amines [43,64,66,220-224], aniline [79], imines [225], or pyrroles [226]. Strong nucleophiles can also lead to a dealkylation of methoxy-substituted carbene complexes (5 2 at the methyl group, [227]), in the same way as methyl esters can be cleaved by nucleophiles such as iodide. Carbon... [Pg.35]

By treatment with NaBH4 in aqueous NaOH in the presence of dithienyl ditelluride, a-phenylseleno carboxylic esters and malonates, as well as a-phenylseleno carboxylic acids, are deselenylated to the corresponding seleno-lree acids in good yields. The selective removal of the seleno group without dealkylation of the ester moiety is achieved by the methods depicted in the scheme. [Pg.127]

Common esters such as alkyl and benzyl carboxylates are easily dealkylated by sodium hydrogen telluride, sodium telluride and sodium ditelluride in DMF. In accordance with a typical S 2 displacement at the aUcoxy group carbon, methyl, ethyl and benzyl esters react smoothly. The nucleophilicity of the reagents is enhanced by the polar aprotic solvent, and the reactivity decreases with higher alkoxy chains due to steric hindrance (e.g. [Pg.155]

The amide type local anesthetic lidocaine is broken down primarily in the liver by oxidative N-dealkylation. This step can occur only to a restricted extent in prilocaine and articaine because both carry a substituent on the C-atom adjacent to the nitrogen group. Articaine possesses a carboxymethyl group on its thiophen ring. At this position, ester cleavage can occur, resulting in the formation of a polar -COO group, loss of the amphiphilic character, and conversion to an inactive metabolite. [Pg.208]

Thus the postulate that a-amino nitrite esters could form and fragment to nitrosamines has provided a useful construct for explaining some aspects of the nitrosative dealkylation of tertiary amines and their derivatives. [Pg.93]

The concave acids 38 and the esters 39 could be interconverted. Reaction of the acids 38 with diazomethane led to the methyl esters 39. 8 2 dealkylation of the esters 39 by lithium iodide in pyridine gave the acids 38 [27]. [Pg.71]

The ax-membered spiro compound 210 reacts with H202/LiBr/HAc to form besides some byproducts the stereoisomeric 4-hydroxy-3 -bromopropyl-phosphinic esters 211 Z and E. This experiment of Stade strengthens the proposed mechanism for oxidative dealkylation formulated above. [Pg.125]


See other pages where Dealkylation esters is mentioned: [Pg.467]    [Pg.505]    [Pg.204]    [Pg.218]    [Pg.467]    [Pg.505]    [Pg.204]    [Pg.218]    [Pg.199]    [Pg.231]    [Pg.379]    [Pg.96]    [Pg.100]    [Pg.40]    [Pg.105]    [Pg.46]    [Pg.66]    [Pg.92]    [Pg.170]    [Pg.249]    [Pg.122]    [Pg.128]    [Pg.1592]    [Pg.156]    [Pg.197]    [Pg.247]    [Pg.34]    [Pg.587]    [Pg.365]    [Pg.91]    [Pg.132]   
See also in sourсe #XX -- [ Pg.13 ]




SEARCH



Dealkylation

Dealkylation of esters

Dealkylations

Esters cleavage via SN2-type dealkylation

© 2024 chempedia.info