Oxidation, alkyl selectivity

Hydrobromic acid is used in the preparation of inorganic bromide salts. The acid also is used for many organic syntheses, including alkyl bromides from alcohols or olefins, and bromophenols from phenols. The compound also is used as an acid catalyst in many alkylation, selective oxidation, isomerization, and dehydrogenation reactions. Other apphcations are in extraction of minerals and use as a reducing agent. 

Methyl (2E,4E)Senoates. The dianion (2) of 1 can be prepared by treatment with I.DA and then sec-butyllithium in THF at —78°. The dianion is alkylated selectively at the a-allylic position to give 3 as the major product. Treatment of 3 with LDA induces a [2,3]sigmatropic rearrangement to 4. Remaining steps to the diunsaturated ester (6) are methylation, oxidation, and dchydrosulfcnylation.1... 

X-ray structures reveal tridentate coordination of L (through the italicized donors) and the existence of intramolecular H-bonding.1088,1089 Interestingly, dinuclear ci5-[Mo(CO)4]2L is produced when (494) reacts with Mo(CO)6.1088 Although displaying a quasi-reversible electrochemical oxidation, complexes of (493) are not amenable to chemical oxidation.1089 Selective mono-alkylation of cyclen and cyclam is facilitated by binding to the Mo(CO)3 moiety (see lead-in references for details1090 1091). 

Paraffin oils, the silicone oils, the medium to long chain alkyl phthalates and isoph-thalates, and the polypropylene oxides are selected for preparation of blowing agent mas-terbatch for making of polystyrene foams. The amoimt of plasticizer should be selected to maintain Vicat softening temperature between 30 and 50°C. 

As an example, this apply to enols or tautomeric enols such as maleic acid derivatives. While with a chemical reagent (cerium ammonium nitrate) the only process occurring is oxidative dimerization, when aromatic nitriles are used as the photochemical oxidant, selective trapping of the radicals by an electrophilic alkenes or by the nitrile itself occurs. Under these conditions, both the alkylation of alkenes and the oxidative alkylation/dimerization of dienes have been smoothly obtained (see Scheme 8) and side processes such as double alkylation or polymerization often occurring with other methods have been avoided. A three-component (Nucleophile-Olefin Combination, Aromatic Substitution) process is also possible. ... 

Alkylation of phenol with methanol is effectively cattJyzed by calcium phosphate which is much more active than boron phosphorous oxide. The selectivity to ortho methylation products, o-cresol and 2,6-xylenol, is 88%. The high selectivity is caused by the basic properties on the surface,... 

Primary Amines—Several new and improved methods for the preparation of aromatic primary amines have been described. " The catalytic reduction of aromatic nitro-compounds to amines with hydrazine hydrate in the presence of iron(iii) oxide hydroxide proceeds smoothly and in high yields. Nitroarenes (1) react with Grignard reagents in the presence of copper(i) iodide, and are alkylated selectively on the aromatic moiety, accompanied by reduction of the nitro-group to the amine (Scheme 1). Both aryl and alkyl azides are rapidly... 

Organotin ethers continue to be employed in selective alkylations. In a study of the Bu2SnO-mediated alkylation of lactosides 1 and 2 aimed at obtaining the 3 -0-ethers, the penta-benzyl ether 2 afforded better yields than the corresponding benzoate 1, and siniilar conditions have been employed for the regioselective benzylation of octyl P-D-galactopyianoside at 0-3 Dibutyltin dimethoxide has been used in place of dibutyltin oxide for selective alkylation of carbohydrate diols. ... 

The synthesis of the linker starts with resin-bound sulfinate 462 that is alkylated firstly with bromobenzylbromide 463 and secondly with propylene oxide 464. Selective monoalkylation has been achieved for both steps and the resulting alcohol 465 was oxidized via Swern oxidation yielding ketone 466. The basic conditions of Swern oxidation are in this case sufficient for elimination and thus a,/3-unsaturated ketones 467 are released from the resin. By slight variation of the aliphatic resin-bound compound, Kurth et al. proved the success of the oxidation/elimination model for the release of cyclic derivatives like cyclopentenones [290]. 

The alkyl derivatives of thiazoles can be catalytically oxidized in the vapor phase at 250 to 400°C to afford the corresponding formyl derivatives (21). Molybdenum oxide, V2O5, and tin vanadate are used as catalysts either alone or with a support. The resulting carbonyl compounds can be selectively oxidized to the acids. 

The selectivity to alcohol in LPO may be significantly increased when boric acid, meta-hotic acid, or boric anhydride is present in stoichiometric amounts (2). The boron compounds appear to convert alkyUiydroperoxides to alkyl borates and may also intercept alkylperoxy radicals, converting them to alkylperoxyboron compounds these are later converted to alkyl borates. The alkyl borates are resistant to further oxidation they are hydrolyzed to recover alcohols. 

Transesterification of methyl methacrylate with the appropriate alcohol is often the preferred method of preparing higher alkyl and functional methacrylates. The reaction is driven to completion by the use of excess methyl methacrylate and by removal of the methyl methacrylate—methanol a2eotrope. A variety of catalysts have been used, including acids and bases and transition-metal compounds such as dialkjitin oxides (57), titanium(IV) alkoxides (58), and zirconium acetoacetate (59). The use of the transition-metal catalysts allows reaction under nearly neutral conditions and is therefore more tolerant of sensitive functionality in the ester alcohol moiety. In addition, transition-metal catalysts often exhibit higher selectivities than acidic catalysts, particularly with respect to by-product ether formation. 

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