Active hydrogen compounds condensation

If the active hydrogen compound has two or three active hydrogens, the Mannich base may condense with one or two additional molecules of aldehyde and ammonia or amine, for example. 

Condensation between carboxylic esters and aldehydes or ketones Condensation between active-hydrogen compounds and aldehydes or ketones (Knoevenagel)... 

Similar reactions of B-hydropyrazaboles with active hydrogen compounds such as pyrocatechol phenol thiols or additional pyrazole are equally facile but require high temperatures (method D). Therefore, the reaction of pyrazabole with o-phenylenediamine may proceed via the expected substituted pyrazabole as an intermediate. However, the latter is unstable under the reaction conditions and condenses further to yield the borazine derivative 10 with the elimination of pyrazole... 

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... 

Interfacial polycondensations can also be carried out in vapor-liquid systems. Reaction takes place at the interface between an aqueous solution of a bifunctional active hydrogen compound and the vapor of diacid chloride. Interfacial condensation is commercially important in the synthesis of polycarbonates (1-52). Polymerizations based on diacids are always less expensive than those that use diacid chlorides. In the polycarbonate case, however, the parent reactant, carbonic acid, is not suitable and the derived acid chloride, phosgene (COCI2), must be used. 

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. 

Reaction of 1,3-dienes tith active hydrogen compounds. The catalyst resulting from the combination of nickel bromide and a dialkoxyphenylphosphine effects condensation of 1,3-dienes with active hydrogen compounds to give butenyl and octadienyl adducts.1 Thus the reaction of morpholine (1, 0.05 mole) with butadiene (0.15 mole) in the presence of nickel bromide (1 mmole) and diisopropoxyphenylphosphine (1.1 mmole) at 100° for 30 min. gives a 79% conversion to the adducts (2), (3), (4), and (5). 

Catalytic activity. Diazoalkanes, in particular phenyldiazomethane. catalyze the condensation of active hydrogen compounds, for example methyl salicylate (1), with isocyanates and isothiocyanates. The primary adduct (2) undergoes cycliza-tion to (3). The rate of the catalyzed reaction parallels the proton mobility of the... 

Mannich reaction.2 This reaction involves the condensation of an active hydrogen compound with formaldehyde and ammonia or a primary or secondary amine (usually as the hydrochloride) ... 

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... 

These reactions can be divided into two categories. They are additions to compounds with active hydrogens and self-condensations. The reactions are well described in organic chemistry textbooks, so there is little reason to describe them here. It is noteworthy, though, that the uncatalyzed reactions of isocyanates with various active hydrogen compounds are probably broadly similar. Among them, the most investigated reactions are those of alcohols with isocyanates... 

A Knoevenagel condensation is a nucleophilic addition of an active hydrogen compound such as malonates to a carbonyl group followed by a dehydration reaction in which a molecule of water is eliminated (hence condensation). The product is an alpha, beta conjugated enone. 

Condensations in which the active hydrogen compound is a )3-keto ester or a )S-diketone often )deld products that result from one molecule of aldehyde or ketone and two molecules of the active methylene component. For example. 

The LDOs as catalysts are also very effective in the Knoevenagel reaction, i.e., cross-aldol condensation of a carbonylic compound with an active hydrogen compound, as shown in following equation (539,545-548)) ... 

The acetoacetic ester condensation (involving the acylation of an ester by an ester) is a special case of a more general reaction term the Claisen condensation. The latter is the condensation between a carboxylic ester and an ester (or ketone or nitrile) containing an a-hydrogen atom in the presence of a base (sodium, sodium alkoxide, sodamide, sodium triphenylmethide, etc.). If R—H is the compound containing the a- or active hydrogen atom, the Claisen condensation may be written ... 

Compounds with active hydrogen add to the carbonyl group of acetone, often followed by the condensation of another molecule of the addend or loss of water. Hydrogen sulfide forms hexamethyl-l,3,5-trithiane probably through the transitory intermediate thioacetone which readily trimerizes. Hydrogen cyanide forms acetone cyanohydrin [75-86-5] (CH2)2C(OH)CN, which is further processed to methacrylates. Ammonia and hydrogen cyanide give (CH2)2C(NH2)CN [19355-69-2] ix.orn. 6<55i the widely used polymerization initiator, azobisisobutyronitrile [78-67-1] is made (4). 

Phthaleins. Dyes of this class are usually considered to be triaryhnethane derivatives. Phenolphthalein [77-09-8] (23, R = CO) and phenol red [143-74-8] (23, R = SO2) are used extensively as indicators in colorimetric and titrimetric determinations (see Hydrogen-ION activity). These compounds are prepared by the condensation of phenol with phthaUc anhydride or i9-sulfoben2oic anhydride, respectively, in the presence of a dehydrating agent. 

Isatin (190) is a compound with interesting chemistry. It can be iV-acetylated with acetic anhydride, iV-methylated via its sodium or potassium salt and O-methylated via its silver salt. Oxidation of isatins with hydrogen peroxide in methanolic sodium methoxide yields methyl anthranilates (81AG(E)882>. In moist air, O-methylisatin (191) forms methylisatoid (192). Isatin forms normal carbonyl derivatives (193) with ketonic reagents such as hydroxylamine and phenylhydrazine and the reactive 3-carbonyl group also undergoes aldol condensation with active methylene compounds. Isatin forms a complex derivative, isamic acid (194), with ammonia (76JCS(P1)2004). 

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