5.17- -substituted with lead salts

In the case of the basic lead salts, the small degree of ring substitution and the low level of methylol/ether/methylene content indicates that formaldehyde has been consumed by a side reaction. The more acidic anions, on the other hand, produce large amounts of methylene linkages. Efficient production of benzylic ether linkage, however, is obtained with lead salts of perffuoro carboxylic acids. 

Terminal alkyne anions are popular reagents for the acyl anion synthons (RCHjCO"). If this nucleophile is added to aldehydes or ketones, the triple bond remains. This can be con verted to an alkynemercury(II) complex with mercuric salts and is hydrated with water or acids to form ketones (M.M.T. Khan, 1974). The more substituted carbon atom of the al-kynes is converted preferentially into a carbonyl group. Highly substituted a-hydroxyketones are available by this method (J.A. Katzenellenbogen, 1973). Acetylene itself can react with two molecules of an aldehyde or a ketone (V. jager, 1977). Hydration then leads to 1,4-dihydroxy-2-butanones. The 1,4-diols tend to condense to tetrahydrofuran derivatives in the presence of acids. 

Direct sulfonation of thiazole, as well as of 2-substituted thiazoles, leads mostly to substitution m the 5-position (330-332). 4-Thiazole sulfonic acid has been prepared through direct sulfonation of 2.5-dibromothiazole with subsequent Rane% Ni reduction (330). Sulfonation of 2.5-dimethyl- and 2-piperidyl-5-methylthiazoles affords the corresponding 4-sulfonic acids as barium salts (247). The 2-hydroxy group facilitates the sulfonation (201. 236). When the 4- and 5-positions are occupied direct sulfonation can occur in the 2-position. 5-hydroxyethyl-4-methyl-2-thiazole sulfonic acid has been prepared in this manner (7). 

Magnesium oxide is a typical acid scavenger for chlorinated mbbers. Compounds containing zinc oxide or magnesium oxide may tend to swell upon immersion in water. These inorganic salts have some water solubiHty and osmotic pressure causes the vulcanizates to imbibe water to equalize pressure (8,9). As such, vulcanizates tend to sweU more in fresh (distilled) water than in salt water. To minimize water sweU, insoluble salts such as lead oxides can be substituted. Because of the health concerns associated with lead, there is much mbber industry interest in other acid acceptors, such as synthetic... 

Oxaziranes derived from isobutyraldehyde react with ferrous salts to give only substituted formamides fEq. (23)], The chain propagating radical 30 thus suffers fission with elimination of the isopropyl group. An H-transfer would lead to substituted butyramides, which are not found. Here is seen a parallel to the fragmentation of alkoxyl radicals, where the elimination of an alkyl group is also favored over hydrogen. The formulation of the oxazirane fission by a radical mechanism is thus supported. 

In aqueous solution especially, the current yield is distinctly lower furthermore, solubility problems can occur when the salt-deficit method is used. In aqueous solution, a-amino- or a-phenyl substituted carboxylates lead mainly to decomposition products, whilst in dry methanol or methanol-pyridine, coupling products were obtained with a-phenyl- and a-acetylaminocarboxylates [49]. 

A thio-substituted, quaternary ammonium salt can be synthesized by the Michael addition of an alkyl thiol to acrylamide in the presence of benzyl trimethyl ammonium hydroxide as a catalyst [793-795]. The reaction leads to the crystallization of the adducts in essentially quantitative yield. Reduction of the amides by lithium aluminum hydride in tetrahydrofuran solution produces the desired amines, which are converted to desired halide by reaction of the methyl iodide with the amines. The inhibitor is useful in controlling corrosion such as that caused by CO2 and H2S. 

The nitrolysis of substituted methylenediamines with nitronium salts can lead to a number of products depending on the nature of the substituents within the substrate. Electron-withdrawing or resonance-stabilizing groups favour the expulsion of an immonium ion and the formation of a secondary nitramine in yields between 58 % and 78... 

Another drawback of RCM applies in case of certain substitution patterns that lead to preferential complexation of the catalyst by substrate functional groups, thereby rendering it inactive. This may be overcome either by a more active or different catalyst or by precomplexation of the donor groups, e.g. with titanium salts [41]. 

If l,l-bis-dimethylamino-2.4.6-triphenyl-X -phosphorin 164 is allowed to react with 2 moles of trifluoroacetic acid and a 10-fold molar excess of methanol in refluxing benzene, one of the amino groups is displaced and 1-methoxy-l-dimethyl-amino-2.4.6-triphenyl-X -phosphorin 757 can be isolated in good yield. The phos-phonium salt 165 (H can also attack C-2) is initially formed by protonation of 164 at C-4 (or C-2). Nucleophilic substitution then leads to 167 via 166 (Hettche, >). 

If an N-substituted hydrazone is used, a quaternary triazolopyridinium salt (13) is the product. Such oxidations have been performed with lead tetraacetate,15 with A/-bromosuccinimide,16 or electrochemically.17... 

Arenediazonium salts substituted with electron-donating groups are good candidates for photoaffinity probes.111191 Photoactivation of these salts leads to the corresponding aryl cations (Scheme 10), which can be stabilized by electron-donating groups at the 2- and 4-posi t ions J11191... 

Phenyl isothiocyanate may be prepared in quantity (Expt 6.98, Method 2) by allowing aniline to react with carbon disulphide to form phenyldithiocarbamic acid (cf. 1), which is isolated as the ammonium salt. Treatment of the latter with lead nitrate removes the elements of hydrogen sulphide to produce phenyl isothiocyanate. As indicated in the preparation of p-bromophenyl isothiocyanate which is given as a further example, a slightly modified procedure which requires the use of rectified spirit as a reaction solvent is necessary in order to obtain good yields of isothiocyanates from substituted anilines. 

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