Carbonyl group with water

Dinitrophenylhydrazine reacts with carbonyl groups with the elimination of water to yield hydrazones (I) and with aldoses or ketoses to yield colored osazones (II). 

Bicyclo[3.2.0]heptane-l,5-diols are oxidized by Jead(IV) acetate35,36 or sodium periodate35 to give cycloheptane-1,4-diones. With lead(IV) acetate in acetic acid at 100 C substrates with a hydroxy group in -position to one of the newly formed carbonyl groups eliminate water to afford a,/ -unsaturated cycloheptanediones,36 and / ,y-double bonds migrate to the apposition.35... 

Obviously, the condensation of a carbonyl group with a diol produces 1 mol of water and because of the reversibility of the reaction (hydrolysis of the acetal), yields are lowered if this by-product is not removed. For such a purpose, there are essentially two possibilities (1) the continuous removal of water by an azeotropic distillation with a solvent mainly chosen for its boiling point (petroleum ether, benzene, toluene, xylene, for instance) (2) the presence of a desiccant (the most commonly taken is copper(II)sulfate, but sodium sulfate or molecular sieves have been also used) molecules known to be water scavengers, such as ortho-esters or dialkylsulfites, have also been suggested, even if they are seldom used in carbohydrate chemistry. 

An unshared pair of electrons on another hydroxy group reestablishes the carbonyl group, with the loss of a water molecule. 

Addition of Alcohols, Water, and Amines. In general, additions to nitriles resemble additions to carbonyl groups with the exception that the primary addition products of simple molecules such as alcohols, water, and ammonia result in the formation of somewhat more stable compounds. Alcohols, for example, react with nitriles in the presence of an acidic catalyst to form salts of imino ethers ... 

An aqueous solution of glyoxylic acid reacts with cyclopentadiene to provide a-hydroxy-y-lactones the more acidic the solution, the faster the reaction (Scheme 13) [68]. Thus at pH 0.9 (2.25 M glyoxylic acid solution in water) the reaction is complete after 90 min at 40 °C providing a 83 % yield of a-hydroxy-y-lactones. In the case of cyclohexadiene, the reaction is complete after 2 days at 90 °C in water, compared to 21 h at 120 °C for the reaction with butyl glyoxylate in neat conditions (Scheme 13). These results show that it is possible to exploit the die-nophilic character of a carbonyl group in water in spite of its quasi total hydration. Pyruvaldehyde, glyoxal, and even ketones like pyruvic acid, also react with dienes in water [69]. 

In this case, diethylenetriamine acts as a trinucleophile its interaction with amino enone 71 involves double nucleophilic addition at the /1-carbon, forming ammonia, and an attack at the carbonyl group, liberating water. The reaction takes place when the compound contains a polyfluoroalkyl substituent, not only enhancing the electrophilicity of the /1-carbon atom, but also stabilizing the imidazolidine ring. 

Dialkyl acylphosphonates are sensitive to water in neutral and alkaline conditions and hydrolyse rapidly to the corresponding carboxylic acids and to dialkyl hydrogen-phosphonate (equation 47) This occurs following the rapid addition of water to the carbonyl group with the formation of stable hydrates. The involvement of stable carbonyl hydrates in the hydrolysis of dimethyl acetylphosphonate and aroylphosphonates was established by H NMR and UV spectroscopy, respectively. In the latter case, the rates of formation and decomposition of the tetrahedral carbonyl hydrates were also determined. 

A great variety of methods is available for the ring synthesis of pyridines the most obvious approach is to construct a 1,5-dicarbonyl compound, preferably also having further unsaturation and allow it to react with ammonia, addition of which at each carbonyl group, with losses of water, producing the pyridine. 1,4-Dihydropyridines, which can easily be dehydrogenated to the fully aromatic system, result from the interaction of aldehydes with two mol equivalents of 1,3-diketones (or 1,3-keto-esters, etc.) and ammonia aldol and Michael reactions and addition of ammonia at the termini, produces the heterocycle. 

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