Alcohols symmetrical

Reductive Etherification. As indicated earlier, aldehydes as well as ketones often give very good yields of ethers when they are treated with Br0nsted acids or other electrophilic species in the presence of organosilicon hydrides (Eq. 172). In the absence of added alcohols, symmetrical ethers are obtained. 

Probl6m 9.11 Draw the organic product of each reaction and classify the product as an alcohol, symmetrical ether,... 

Raney nickel modified with Mg or V can be used for the highly selective preparation of symmetrical amines by the alkylation of ammonia with n-propanol or i-butanol. Upon modifying the Raney nickel catalyst with 0.5 wt % V or Mg, 4-5 % increase in the selectivity to secondary amines was observed and the selectivities reached 70-80 % at 90-95 % conversions. In the alkylation of ammonia with an alcohol symmetrical secondary amines can be obtained with 70 % yield over Mg or V modified Raney nickel catalyst at 220-240 °C and ammonia/alcohol ratio of 1.5. In an industrial application 2-4 % increase of the selectivity results in an important finantial benefit. It was shown that pure (100 %) ethylamine and 70 % EtNH2 in water can be used for the preparation of N-ethyl-N-butylamine over a commercial Cu0-Zn0-Al203 catalyst. 

The term acjdoin is commonly used as a class name for the symmetrical keto-alcohols RCOCH(OH)R, and the name of the individual compound Is derived by adding the suffix oin to the stem name of the acid to which the acyloin corresponds, e.g., acetoin, propionoin, butyroin, etc. 

In stereoselective antitheses of chiral open-chain molecules transformations into cyclic precursors should be tried. The erythro-configurated acetylenic alcohol given below, for example, is disconnected into an acetylene monoanion and a symmetrical oxirane (M. A. Adams, 1979). Since nucleophilic substitution occurs with inversion of configuration this oxirane must be trens-conilgurated its precursor is commercially available trans-2-butene. 

In general this method is limited to the preparation of symmetrical ethers m which both alkyl groups are primary Isopropyl alcohol however is readily available at low cost and gives high enough yields of diisopropyl ether to justify making (CH3)2CHOCH(CH3)2 by this method on an industrial scale... 

Diorgano Sulfites. Symmetrical or mixed dialkyl sulfites ate prepared by the stepwise reaction of thionyl chloride either with two molecules of an alcohol or with stoichiometric quantities of two alcohols in pyridine (105). 

Alcohol dehydrogenase-catalyzed reduction of ketones is a convenient method for the production of chiral alcohols. HLAD, the most thoroughly studied enzyme, has a broad substrate specificity and accommodates a variety of substrates (Table 11). It efficiendy reduces all simple four- to nine-membered cycHc ketones and also symmetrical and racemic cis- and trans-decalindiones (167). Asymmetric reduction of aUphatic acycHc ketones (C-4—C-10) (103,104) can be efficiendy achieved by alcohol dehydrogenase isolated from Thermoanaerohium hrockii (TBADH) (168). The enzyme is remarkably stable at temperatures up to 85°C and exhibits high tolerance toward organic solvents. Alcohol dehydrogenases from horse Hver and T. hrockii... 

Alcohols can be dehydrated with strong acid catalysts and high reaction temperatures to produce ethers. This method is particularly useful for the preparation of symmetrical lower alkyl ethers, such as ethyl ether. 

Sylvestrene tetrabromide, CjoHjf.Br, is prepared when pure sylvestrene, regenerated from its ihydrochloride and dissolved in acetic acid, is heated with bromine until a permanent yellow colour is produced. Water is added to the reaction product, but not sufficient to precipitate the bromide, and the vessel allowed to stand in a cold place. The bromide separates and can be purihed by recrystallisation from alcohol. It forms mono-symmetric crystals melting at 135° to 136°, and having a specihc rotation -t- 73 7°. 

As a symmetrical ketone, acetone is a reactive compound with many synthetic uses. Among the important chemicals based on acetone are methylisobutyl ketone, methyl methacrylate, ketene, and diacetone alcohol. 

Methyl-2-hexcne has a disubstituted double bond, RCH=CHR, and would probably give a mixture of two alcohols with either hydration method since Markovnikov s rule does not apply to symmetrically substituted alkenes. 3-MethyI-3-hexene, however, has a trisubstituted double bond, and would give only the desired product on non-Markovnikov hydration using the hydroboration/oxidation method. 

Diethyl ether and other simple symmetrical ethers are prepared industrially by the sulfuric acid-catalyzed dehydration of alcohols. The reaction occurs by SN2 displacement of water from a protonated ethanol molecule by the oxygen atom of a second ethanol. Unfortunately, the method is limited to use with primary alcohols because secondary and tertiary alcohols dehydrate by an El mechanism to yield alkenes (Section 17.6). 

Problem 18.2 Why do you suppose only symmetrical ethers are prepared by the sulfuric add-catalyzed dehydration procedure What product(s) would you expect if ethanol and 1-propanol were allowed to react together In what ratio would the products be formed if the two alcohols were of equal reactivity ... 

The C2-symmetric epoxide 23 (Scheme 7) reacts smoothly with carbon nucleophiles. For example, treatment of 23 with lithium dimethylcuprate proceeds with inversion of configuration, resulting in the formation of alcohol 28. An important consequence of the C2 symmetry of 23 is that the attack of the organometallic reagent upon either one of the two epoxide carbons produces the same product. After simultaneous hydrogenolysis of the two benzyl ethers in 28, protection of the 1,2-diol as an acetonide ring can be easily achieved by the use of 2,2-dimethoxypropane and camphor-sulfonic acid (CSA). It is necessary to briefly expose the crude product from the latter reaction to methanol and CSA so that the mixed acyclic ketal can be cleaved (see 29—>30). Oxidation of alcohol 30 with pyridinium chlorochromate (PCC) provides alde-... 

Jacobsen demonstrated that the (salen)Cr system used to effect intermolecular, cooperative asymmetric azidolysis of meso-epoxides (Schemes 7.3 and 7.5) could be applied to sulfur-centered nucleophiles (Scheme 7.13). In order to overcome moderate enantioselectivity (<60% ee), a dithiol nucleophile was employed as part of a double resolution strategy in which the minor enantiomer of the monoaddition product reacts preferentially to form the meso- bis-addition product, thereby increasing the ee of the C2-symmetric bis-addition product. Enantiopure 1,2-mer-capto alcohols (>99% ee) were obtained from the meso-epoxide in ca. 50% overall yield by a burdensome (though effective) multistep sequence, [23]. 

Lithiated (5)- or r c-(tm-butylsulfinylmethyl)benzene adds to acetone68, benzophenone69, or other symmetrical carbonyl compounds8- 70, respectively, to yield a single diastereomeric alcohol. 

Although this material contains a small amount of the symmetrical dihydrazide, which is not easily eliminated on crystallization, it is entirely satisfactory for use as a reagent for the isolation of ketones. A purer product, m. p. 192°, with decomposition, can be obtained by adding the solution prepared from ethyl chloroacetate and trimethylamine to an alcoholic solution containing a considerable excess of the hydrazine hydrate. 

The foaming properties of sodium symmetrical secondary alcohol sulfates, sodium secondary alcohol sulfates, isomeric sodium secondary pentanol sulfates, and sodium linear alcohol sulfates were studied by Dreger et al. [72] via the Ross-Miles test [150] at 46°C. Within the linear series sodium tetradecyl sulfate produces the largest amount of foam. The influence of several electrolytes was also studied. 

Application of the bromine substitution reaction allows the synthesis of aminoamides, alkoxyamides of simple alcohols and sugars, depsipeptides and (NH) pseudopeptides, C2 symmetric compounds. 

Allylic or benzylic alcohols can be symmetrically coupled by treatment with... 

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