Nonacidic media

Halogenation of pyridines is easier than nitration or sulfonation because it can be carried out in nonacidic media and the pyridinehalogen adducts are appreciably dissociated. Dihalogenation can occur since one halogen atom causes little additional deactivation of the ring. The mercuration of pyridines (Section 3.2.1.4.9) probably involves initial coordination of the pyridine nitrogen to the mercury atom, and such coordination causes less ring deactivation than N-protonation. 

Improved understanding of the mechanism of palladium-induced dehydrogenations has led to the development of significantly better catalysts and reaction conditions. In particular, mixtures of PdCl2(PhCN)2 and silver triflate in the presence of -methylmorpholine have allowed the efficient dehydrogenation of aldehydes under ambient conditions and in nonacidic media (equation 18). Ketones undergo a similar reaction, affording enones in 60-78% yield, but require prior formation of the tin enol-ate with tin(II) triflate.Under these conditions, however, 2 equiv. of palladium(II) chloride were used to effect conversion, which severely limits the usefulness of the method. 

Unsubstituted ketoximes undergo rearrangement in nonacidic media also. Thus, both geometric isomers of cholest-4-en-3-one oxime (12) rearranged to (13) in the presence of triphenylphosphine in refluxing tetrachloromethane (equation 8) 7 the apparent reluctance to migrate of endocyclic unsaturated substituents has also been observed for 0-substituted oximes (vide infra). 

Levy and coworkers97 have measured 13C spin-lattice relaxation times, 7), for 3- and 4-aminobiphenyls in a number of solvent systems, and of the corresponding ammonium ions in acidic and nonacidic media. The observed 7) values indicated that the molecular tumbling is anisotropic for these species. In addition, the known biphenyl geometry allowed indentification and semiquantitative evaluation of internal rotation-libration motion. The protonated amine function is motionally more restricted by solvent-solute and ion-pair interactions than the corresponding neutral amine. Thus, in the 3-biphenylammonium ion, the principal axis for molecular reorientation is aligned close to the C3—NHj-bond, whereas in the amine the principal axis lies closer to the biphenyl C2-symmetry axis. In both 3- and 4-aminobiphenyls, the unsubstituted phenyl rings are less restricted due to rapid phenyl rotation or libration. Table 14 presents 13C Tj-data for 4-aminobiphenyl 37 (NH2 on C4) and 4-biphenylammonium acetate 38 and trifluoroacetate 39. 

Derivatives Soluble in Nonacidic Media and Organic Solvents. - 255... 

Aryl Azides in Nonacidic Media The Chemistry of Singlet Aryl Nitrenes 44-5... 

Reactions of 2-aminopyridines with /i-chlorovinyl ketones were surveyed by Fischer.16 He established that in a nonacidic medium (acetone-methanol mixture) the pyridinium salts (7) are formed, which can then be cyclized by acids (acetic acid and 70% perchloric acid) to the 2-substituted pyrido[l,2- ]-pyrimidinium salts (10).1415 in acidic media, however, the 4-substituted pyrido[l,2-a]pyrimidinium salts (9) are formed via the enamine (8).616... 

Corrosion inhibitors are an important chemical constituent of Cu CMP slurry. The critical performance of a slurry such as static etch rate, material removal rate, and post-CMP defect counts are greatly influenced by the concentration and the structure of the inhibitor used in the slurry. BTA is proven to be an effective corrosion inhibitor for Cu CMP especially in nonacidic medium. 

Monohalogenated products are obtained by treatment of this heterocycle (20) with elemental halogens (bromine, chlorine, or iodine) in concentrated sulfuric acid containing silver sulfate. This acidic reaction medium aids electrophilic attack by the positive halogen species on a protonated thienopyridine. Subsequently, nonacidic conditions have been identified for the monobromination reaction <74JHC205>. Monobromination of the isomers (21) and (23) has also been reported <70AK(32)249>. 

Sommelet reaction This reaction also involves reaction of a halide, usually a benzyl-type halide, with hexamine to form a heximinium salt, which is then hydrolyzed in a nonacidic aqueous medium such as water or aqueous alcohol. In the procedure formulated, the reaction of benzyl chloride with hexamine is carried out... 

The ease of formation of (1) from (2) depends, among other factors, on the nature of the leaving group. The only systematic study pertains to 4-substituted azetidinones, where the order of reactivity Cl > RCO2 > RSO2 > N3 > RO > RS was found for substitution reactions under nonacidic conditions. In an acidic medium this order will very likely be different. 

For the canning of certain types of nonacid fruits and vegetables the canning medium must be low in acid-forming thermophilic bacteria. Specifications issued by the National Canners Association (2) are easily met by the competent producers of either medium. 

Initially, most or even all known MALDI matrices were acidic compounds, such as benzoic and cinnamic acid derivatives. However, the acidic medium is not well-suited to keeping noncovalently bound complexes intact. In the 1990s, a couple of groups therefore introduced a number of nonacidic MALDI matrices such as 2-amino-4-methyl-5-nitropyridine, />ara-nitroaniline, or 6-aza-2-thio-thymine. These were shown to be beneficial for MALDI MS of noncovalent complexes—for example, to keep peptide-oligonucleotide complexes or DNA duplexes intact.However, their performance at high molecular... 

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