Ketones, reaction with water

The zwitterion (6) can react with protic solvents to produce a variety of products. Reaction with water yields a transient hydroperoxy alcohol (10) that can dehydrate to a carboxyUc acid or spHt out H2O2 to form a carbonyl compound (aldehyde or ketone, R2CO). In alcohoHc media, the product is an isolable hydroperoxy ether (11) that can be hydrolyzed or reduced (with (CH O) or (CH2)2S) to a carbonyl compound. Reductive amination of (11) over Raney nickel produces amides and amines (64). Reaction of the zwitterion with a carboxyUc acid to form a hydroperoxy ester (12) is commercially important because it can be oxidized to other acids, RCOOH and R COOH. Reaction of zwitterion with HCN produces a-hydroxy nitriles that can be hydrolyzed to a-hydroxy carboxyUc acids. Carboxylates are obtained with H2O2/OH (65). The zwitterion can be reduced during the course of the reaction by tetracyanoethylene to produce its epoxide (66). 

The ketocarbene 4 that is generated by loss of Na from the a-diazo ketone, and that has an electron-sextet, rearranges to the more stable ketene 2 by a nucleophilic 1,2-shift of substituent R. The ketene thus formed corresponds to the isocyanate product of the related Curtius reaction. The ketene can further react with nucleophilic agents, that add to the C=0-double bond. For example by reaction with water a carboxylic acid 3 is formed, while from reaction with an alcohol R -OH an ester 5 is obtained directly. The reaction with ammonia or an amine R -NHa leads to formation of a carboxylic amide 6 or 7 ... 

Aldehydes and ketones react with water to yield 1,1-diols, or geminal (gem) diols. The hydration reaction is reversible, and a gem diol can eliminate water to regenerate an aldehyde or ketone. 

When calcium carbonate goes into solution, it releases basic carbonate ions (COf ), which react with hydrogen ions to form carbon dioxide (which will normally remain in solution at deep-well-injection pressures) and water. Removal of hydrogen ions raises the pH of the solution. However, aqueous carbon dioxide serves to buffer the solution (i.e., re-forms carbonic acid in reaction with water to add H+ ions to solution). Consequently, the buffering capacity of the solution must be exceeded before complete neutralization will take place. Nitric acid can react with certain alcohols and ketones under increased pressure to increase the pH of the solution, and this reaction was proposed by Goolsby41 to explain the lower-than-expected level of calcium ions in backflowed waste at the Monsanto waste injection facility in Florida. 

Although the high reactivity of metal-chalcogen double bonds of isolated heavy ketones is somewhat suppressed by the steric protecting groups, Tbt-substituted heavy ketones allow the examination of their intermolecular reactions with relatively small substrates. The most important feature in the reactivity of a carbonyl functionality is reversibility in reactions across its carbon-oxygen double bond (addition-elimination mechanism via a tetracoordinate intermediate) as is observed, for example, in reactions with water and alcohols. The energetic basis... 

The reactivity of carbohydrates is dominated by the reactivity of the aldehyde group and the hydroxyl on its next-neighbor (/ ) carbon. As illustrated by the middle row of Fig. 2.3, the aldehyde can be isomerized to the corresponding enol or be converted into its hydrate (or hemiketal) form upon reaction with water (or with an hydroxyl-group). These two reactions are responsible for the easy cycliza-tion of sugars in five- and six-membered rings (furanose and pyranose) and their isomerization between various enantiomeric forms and between aldehyde- and ketone-type sugars (aldose and ketose). 

A naive look at the product suggests an oxidation to a ketone followed by a Baeyer-Villiger like reaction. The product is best explained by a fragmentation from an intermediate chromate ester, resulting on an aldehyde and a stabilized tertiary carbocation that is transformed into a tertiary alcohol by reaction with water. The hydroxyaldehyde so obtained may evolve to the final lactone either via a lactol or a hydroxyacid. 

Comparisons of structurally related hydroxy- and methoxy-substituted cations show that hydroxy is more stabilizing by between 4 and 5 log units. This difference was recognized 20 years ago by Toullec who compared pifas for protonation of the enol of acetophenone and its methyl ether145 (-4.6 and 1.3, respectively) based on a cycle similar to that of Scheme 15, but with the enol replacing the hydrate, and a further cycle relating the enol ether to a corresponding dimethyl acetal and methoxycarbocation.146 Toullec concluded, understandably but incorrectly, that there was an error in the pA a of the ketone (over which there had been controversy at the time).147,148 In a related study, Amyes and Jencks noted a difference of 105-fold in reactivity in the nucleophilic reaction with water of protonated and O-methylated acetone and concluded that the protonated acetone lacked a full covalent bond to... 

Halogens add to ketones at the alpha carbon in the presence of a base or an arid-When a base is used, it is dffieult to prevent haJogdnation at more than one of the alpha positions. The base is also consumed by the reaction with water as a by-product, whereas the acid acts as a true catalyst and is not consumed. 

Aldol reactions using catalyst 12 were also performed with water without any organic solvent (Table 2.9) [15]. In these examples, it is assumed that the reaction occurred in the organic phase composed of reactants and the catalyst separated from the water phase. A large excess of ketone was used in these reactions. Catalysts possessing a tert-butyldimethylsilyl (TBS) or a triisopropylsilyl (TIPS) group instead of the tert-butyldiphenylsilyl (TBDPS) group on 12 also effectively catalyzed the reaction with water, but hydroxyproline 2 did not catalyze the reaction under the same conditions this indicated that the hydrophobic substituents of... 

Aldehydes and ketones undergo methylenation in 50-85% yield on reaction with either 1 or 2 (2 equiv.) in THF aldehydes react much more rapidly than ketones. Reactions with 1 can also be conducted in ethanol or aqueous THF at -70°, but reagent 2 is much less effective in the presence of ethanol or water. Both reagents are useful for methylenation of substrates contaming hydroxyl groups. Methylenation of o-hydroxybenzaldehyde with 1 in anhydrous THF proceeds in 76% yield. 

Aldehydes and ketones underigo reaction with water to yieM 1,1-dioJr. geminal em> dlols. The hydration reaction is reversible, ond d gem can climinotc water to rsqfencratc a ketorn or aldehyde. 

The mechanism for the oxidation of 1° alcohols to aldehydes parallels the oxidation of 2° alcohols to ketones detailed in Section 12.12A. Oxidation of a 1 alcohol to a carboxylic acid requires three operations oxidation first to the aldehyde, reaction with water, and then further oxidation to the carboxylic acid, as shown in Mechanism 12.6. 

While reaction solvents are not necessary for the process of this invention, suitable solvents may be employed if desired. If solvents are used it is necessary to select solvents which per se are not alkylated, i.e.,those which are inert to the alkylation effects of the dialkyl sulfate. Suitable such non-alkylatable solvents are diethyl ether, dioxane, acetone methyl ethyl ketone, ethyl acetate, butyl acetate, tetrahydrofu-ran, and the like. When the desired compound is recovered by pouring the reaction mixture into water after the completion of the reaction, solvents such as dioxane, acetone and methyl ethyl ketone miscible with water are preferably used. For instance, acetone is preferred. Agitation causes the reaction to proceed rapidly. The reaction time can be varied over a wide range depending upon conditions such as reaction temperature and agitation. For example, the reaction time can vary from several tens of minutes to several days. When the reaction is completed, which... 

The heterocyclic systems of 1,3-oxazinium ions are widely used in the organic synthesis . Thus, 5,6-dihydro-4/f-l,3-oxazines 40, being a cyclic derivative of 1,2-aminoalcohols, can serve as Cj-synthones for the preparation of aldehydes, ketones and carboxylic acids . The 47/-l,3-oxazines 47 can undergo oxidative dehydrogenation by treatment with the trityl salts or benzoquinone to form the 3-azapyrylium salts 48, which then give various jV-acylenamine derivatives 49-52 by reaction with water or with active methylene comjKJunds (equation 18) . 

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