Active hydrogen compounds formation

The great reactivity of the sulfurane prepared by this procedure toward active hydrogen compounds, coupled with an indefinite shelf life in the absence of moisture, makes this compound a useful reagent for dehydrations,amide cleavage reactions, epoxide formation, sulfilimine syntheses, and certain oxidations and coupling reactions. 

Instead of carboxylic acids, other carbonyl compounds can be used acid halides, esters, amides, etc. The commonly accepted general mechanism for these reactions consists of the initial nucleophilic addition of an active hydrogen compound to the electron-poor carbonyl carbon atom of the R COOI I molecule, with the formation of a metastable intermediate that can undergo a subsequent elimination reaction ... 

Although formaldehyde has been most common, other aldehydes have also been used successfully for the formation of iminium ion. The Mannich reaction also proceeds with the other activated hydrogen compounds such as indole, furan, pyrrole and phenols. When primary amine is used, the Mannich base formed is a secondary amine and may undergo further condensation to yield tertiary amine. The Mannich base may eliminate an amine... 

Some of the most familiar reactions falling into the polycondensation class are those leading to polyamides derived from dicarboxylic acids and diamines, polyesters from glycols and dicarboxylic acids, polyurethanes from polyols and polyisocyanates, and polyureas from diamines and diisocyanates. Similar polymer formations utilizing bifunctional acid chlorides with polyols or polyamines also fall into this class. The condensations of aldehydes or ketones with a variety of active hydrogen compounds such as phenols and diamines are in this group. Some of the less familar polycondensation reactions include the formation of polyethers from bifunctional halogen compounds and the sodium salts of bis-phenols, and the addition of bis-thiols to diolefins under certain conditions. 

Morton and Deisz (31) measured the reaction rate of phenyl isocyanate in dioxane at 80° with a variety of active hydrogen compounds and obtained the relative rates as shown by Table I. The high reactivity of carbanilide (leading to the formation of biuret) is worth noting. 

Treatment of [(arene)OsCl2]2 with lithium amide in THF results in the formation of imidoosmium complexes in high yield, which react with a with wide variety of active hydrogen compounds and polar compounds (Scheme 10.28) [253]. 

Isocyanates have some important reactions without the participation of active hydrogen compounds. These reactions, of real importance in polyurethane chemistry are dimerisation, trimerisation, formation of carbodiimides and reaction with epoxides and cyclic anhydrides. 

The complex formed between diethyl azodicarboxylate and triphenylphosphine is a very useful reagent for condensation reactions. The reaction of alcohols with phthalimides, in the presence of diethyl azodicarboxylate and triphenylphosphine, resulted in the formation of the corresponding AT-alkylphthalimide in good yield. The reaction proceeds stereospecifically with complete inversion, as shown by conversion of (5 )-(+)-2-octanol to )-2-octylamine, isolated by treatment of the initially formed phthalimide with hydrazine hydrate. Condensation between alcohols and other active-hydrogen compounds using the same reagents has also been described (Scheme 1). Phosphorylation of alcohols by initial activation... 

Acids influence the NCO/OH reaction by accelerating chain extension a little, and retarding crosslinking. If p-nitrobenzoylchloride is added to a urethane system in which active hydrogen compounds must be present, this additive has a mild catalytic effect on chain extension, no effect on allophanate formation, and a strong retarding effect on biuret formation. If water is present the reaction is strongly catalyzed. 

Reaction of butadiene with aldehydes in the presence of palladium(o)-triphenylphosphine species leads to two products (80) and (81), whose formation can be explained by the mechanism outlined in Scheme 4. Whereas butadiene reacts with active-hydrogen-containing compounds such as a-cyano-esters or jS-diketones in the presence of palladium complexes of unidentate phosphines, in the presence of palladium complexes of bidentate phosphines addition of the butadiene to the active-hydrogen compound takes place. ... 

There are three principal ionic ring-opening polymerization reactions of epoxides acid-initiated, base-initiated, and coordinate-initiated polymerizations. The acid-initiated reaction involves addition of an active hydrogen compound, HY, such as ethanol, to an epoxide ring and is catalyzed by an acid, HX, such as perchloric acid. The reaction sequence involves formation of an oxonium complex, followed by ring opening by an 8 2 cleavage of an oxonium carbon bond. 

Fig. 4. Chiroselective inclusion formation of racemic l-phenylethylammonium salt ((R/S)-14) using optically active crown compound ((i, 5)-13) [53955-48-9]. The diastereomeric inclusion complex (R)-(14) is more stable than (3, 3)-(13)-(3)-(14) (top views, dotted lines represent hydrogen...

The use of polar solvents, such as /V, /V- dim ethyl fo rm am i de [68-12-2] is noted to result in extensive trimer formation. However, if the isocyanate is trapped using compounds such as alcohols, carboxyUc acids, and amines which contain active hydrogen, high yields are obtained (93). 

Various patents (22—24) have been issued claiming the use of tetrakis(hydroxymethyl)phosphonium sulfate in, for example, water treating, pharmaceuticals (qv), and in the oil industry where this compound shows exceptional activity toward the sulfate-reducing bacteria that are a primary cause of hydrogen sulfide formation and consequent problems associated with souring and corrosion (25). 

In addition to their concern regarding spray residues of the lead arsenate and organic types, canners whose fruits are sprayed with lime sulfur have reason for concern over the presence of sulfur in their canned products. The presence of elemental sulfur or simple compounds of reduced sulfur in canned foods, especially in those products having an acid character, is objectionable, not only because it may be the source of sulfide flavor and staining, but also because it may actively accelerate the formation of hydrogen by the corrosive action of the product on the container. 

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