Method aldehydate

Cyanuric chloride method Divinylsulfone method Epoxy (bisoxirane) method Aldehyde groups Hydrazide method Carboxyl groups... 

Related Methods Aldehydes from Ketones (Section 57)... 

The first general synthesis, which has been useful for the preparation of enamines derived from aldehydes, was discovered by Mannich and Davidsen14. According to this method aldehydes and secondary amines react in the cold in the presence of potassium carbonate to give aminals 1 (equation 1). In many cases the aminal becomes the major product15,16 by the use of two equivalents of the amine. Destructive distillation of the aminal then leads to the enamine. Aminals are thermally stable up to temperatures of about 170 °C in the presence of base, and their decomposition to enamines at lower temperatures is acid-catalysed17. 

Brown and coworkers have described an alternative synthesis of chiral alkylboronic esters. In this synthesis prochiral alkenes are hydroborated with monoisopinocamphenylborane to yield isopinocam-phenylalkylboranes which are then readily transformed to chiral alkyllraronic esters (Scheme 39). Homologation with dichloromethyllithium, followed by reduction with potassium triisopropoxyborohy-dride (KIPBH) and oxidation, finely yields B-chiral alcohols (Scheme 40). These alcohols are not easily prepared by other methods. Aldehydes can be prepared by homologation from chiral alkylboronic esters with LiCH(OMe)SPh and oxidation (Scheme 41). ... 

Aren ci2ch-o- R Kataly- Methode Aldehyd Ausbeute Lite-... 

As with covalent coupling methods, aldehyde couphng is well suited to electrostatic concentration conditions, provided the sensor surface holds residual negative charges. 

Reductive Methods.—Aldehydes from Acid Equivalents. In a two-step process which formally constitutes a reduction, carboxylic acids are first reduced to the corresponding alkyl borate ester by the borane-dimethyl sulphide complex, which in turn is oxidized in high overall yield to the aldehyde [equation (1)]. ... 

The properties of fatty aldehydes have been reviewed [303,576]. In the native form, they can be analysed by GC on similar columns to those used for fatty acid analysis, and they can be identified and estimated by analogous procedures. Standard aldehyde mixtures are available from commercial sources, or they can be prepared from the corresponding fatty acids by a number of simple methods. Aldehydes have been reported to be stable for long periods, if stored at -20°C in solution in carbon disulfide or other inert solvents such as pentane or diethyl ether [990], but they should not be kept in contact with other lipids, especially those containing ethanolamine, which catalyses a condensation reaction in which 2,3-dialkylacroleins are formed [805]. 

Reductive Methods.—Aldehydes from Acid Derivatives. Acid chlorides are reduced to aldehydes by sodium borohydride in the presence of cadmium(il)... 

Related methods Aldehydes from Alcohols and Phenols (Section 48)... 

Doebner-von Miller reaction Condensation of an aromatic amine with an aldehyde or ketone in the presence of hydrochloric acid to form a quinoline derivative. A general method, thus aniline and ethanal give 2-methyl-quinoline (quinaldine) and p-phenetidine. 

Here we will illustrate the method using a single example. The aldol reaction between an enol boronate and an aldehyde can lead to four possible stereoisomers (Figure 11.32). Many of these reactions proceed with a high degree of diastereoselectivity (i.e. syn anti) and/or enantioselectivity (syn-l syn-Tl and anti-l anti-lT). Bernardi, Capelli, Gennari,... 

Aldehydes and ketones may be converted into the corresponding primary amines by reduction of their oximes or hydrazones (p. 93). A method of more limited application, known as the Leuckart Reaction, consists of heating the carbonyl compound with ammonium formate, whereby the formyLamino derivative is formed, and can be readily hydrolysed by acids to the amine. Thus acetophenone gives the i-phenylethylformamide, which without isolation can be hydrolysed to i-phenylethylamine. 

Many aldehydes and ketones can be reduced directly by Clenimemen s method, in which the aldehyde or ketone is boiled with dilute hydrochloric acid and amalgamated zinc. />-Methylacetophenone (or methyl />-tolyl ketone) is reduced under these conditions to />-ethyltoluene. An excess of the reducing agent is employed in order to pre ent the formation of unsaturated hydrocarbons. 

Noth. The above method can be successfully applied only to dilute solutions of formaldehyde which are free in particular from other alfphatic aldehydes, since the latter, if present, would undergo a similar oxidation. Formaldehyde, if mixed with other aldehydes, should be estimated by quantitative addition of potassium cyanide for details, see advanced text-books of quantitative organic analysis. 

Small quantities of esters (in the above example n-hexyl n-caproate CH3(CHj)3COO(CH2)jCH3) are simultaneously formed. This is an excellent method for the preparation of aldehydes. 

Oximes. The method given for semicarbazones (see 2) may be employed use 1 g. of hydroxylamine hydrochloride, 2 g. of crystallised sodium acetate and 0 5 g. of the aldehyde or ketone. It is usually advisable to warm on a water bath for 10 minutes. 

An important general method of preparing indoles, known as the Fischer Indole synthesis, consists in heating the phenylhydrazone of an aldehyde, ketone or keto-acld in the presence of a catalyst such as zinc chloride, hydrochloric acid or glacial acetic acid. Thus acrtophenone phenylhydrazone (I) gives 2-phenyllndole (I V). The synthesis involves an intramolecular condensation with the elimination of ammonia. The following is a plausible mechanism of the reaction ... 

This preparation illustrates the method to be adopted for aldehydes of boiling point below about 150°. 

Method 2. Dissolve 0-25 g. of 2 4-dinitrophenylhydrazine in a mixture of 42 ml. of concentrated hydrochloric acid and 50 ml. of water by warming on a water bath dilute the cold solution to 250 ml. with distilled water. This reagent is more suitable for water-soluble aldehydes and ketones since alcohol is absent. 

METHOD 2 [89]--1M MDA or benzedrine and 1M benzaldehyde is dissolved in 95% ethanol (Everclear), stirred, the solvent removed by distillation then the oil vacuum distilled to give 95% yellow oil which is a Schiff base intermediate. 1M of this intermediate, plus 1M iodomethane, is sealed in a pipe bomb that s dumped in boiling water for 5 hours giving an orangy-red heavy oil. The oil is taken up in methanol, 1/8 its volume of dH20 is added and the solution refluxed for 30 minutes. Next, an equal volume of water is added and the whole solution boiled openly until no more odor of benzaldehyde is detected (smells like almond extract). The solution is acidified with acetic acid, washed with ether (discard ether), the MDMA or meth freebase liberated with NaOH and extracted with ether to afford a yield of 90% for meth and 65% for MDMA. That s not a bad conversion but what s with having to use benzaldehyde (a List chemical) Strike wonders if another aldehyde can substitute. 

Terminal alkyne anions are popular reagents for the acyl anion synthons (RCHjCO"). If this nucleophile is added to aldehydes or ketones, the triple bond remains. This can be con verted to an alkynemercury(II) complex with mercuric salts and is hydrated with water or acids to form ketones (M.M.T. Khan, 1974). The more substituted carbon atom of the al-kynes is converted preferentially into a carbonyl group. Highly substituted a-hydroxyketones are available by this method (J.A. Katzenellenbogen, 1973). Acetylene itself can react with two molecules of an aldehyde or a ketone (V. jager, 1977). Hydration then leads to 1,4-dihydroxy-2-butanones. The 1,4-diols tend to condense to tetrahydrofuran derivatives in the presence of acids. 

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