Condensation with active hydrogen

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). 

MEK is a colorless, stable, flammable Hquid possessing the characteristic acetone-type odor of low molecular weight aUphatic ketones. MEK undergoes typical reactions of carbonyl groups with activated hydrogen atoms on adjacent carbon atoms, and condenses with a variety of reagents. Condensation of MEK with formaldehyde produces methylisopropenyl ketone (3-methyl-3-buten-2-one) ... 

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). 

The condensation of aldehydes and ketones with active hydrogen atoms is called Knoevenagel condensation. It is related to an aldol condensation and commonly is used to produce enones (a compound with a carbon-carbon double bond adjacent to a carbonyl). The process requires a weak base (an amine). A typical excimple and mechanism eire presented in Figure 15-22. 

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... 

AU considered condensation reactions have some anomalies for the a,j8-unsaturated carbonyl compounds. Most reagents with active hydrogen atoms can react not only with carbonyl groups but also with polarized conjugated double bonds C = C. As a result of this regularity, three products, instead of the estimated one target derivative, are formed in the reactions of a,)8-unsaturated carbonyl compounds with O-alkyl hydroxylamines ... 

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... 

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 halogen atom directly attached to a benzene ring is usually unreactive, unless it is activated by the nature and position of certain other substituent groups. It has been show n by Ullmann, however, that halogen atoms normally of low reactivity will condense with aromatic amines in the presence of an alkali carbonate (to absorb the hydrogen halide formed) and a trace of copper powder or oxide to act as a catalyst. This reaction, known as the Ullmant Condensation, is frequently used to prepare substituted diphenylamines it is exemplified... 

Formaldehyde may react with the active hydrogens on both the urea and amine groups and therefore the polymer is probably highly branched. The amount of formaldehyde (2—4 mol per 1 mol urea), the amount and kind of polyamine (10—15%), and resin concentration are variable and hundreds of patents have been issued throughout the world. Generally, the urea, formaldehyde, polyamine, and water react at 80—100°C. The reaction may be carried out in two steps with an initial methylolation at alkaline pH, followed by condensation to the desired degree at acidic pH, or the entire reaction may be carried out under acidic conditions (63). The product is generally a symp with 25—35% soHds and is stable for up to three months. 

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