1- butyne hydration

The mechanism described in the textbook Figure 9.6 is adapted to the case of 2-butyne hydration as shown ... 

Give the structure of the enol formed by hydration of 2 butyne... 

Hydration of 2-butyne-l,4-diols (1). Treatment of 1 with acetic anhydride and pyridine (25°) results in acetylation of the less hindered hydroxyl group. When treated with AgC104, the monoacetate (2) is converted into the enol acetate of a dihydro-3(2H (-furanone (3, equation I). The regioisomeric dihydro-3(2H)-furanone is formed by hydration of 1 with Hg(OAc)2-Nafion-H preferentially (equation II).1... 

Hydration of an internal alkyne with strong acid forms an enol by a mechanism similar to that of the acid-catalyzed hydration of an alkene (Section 10.12). Mechanism 11.4 illustrates the hydration of 2-butyne with H2O and H2SO4. Once formed, the enol then tautomerizes to the more stable keto form by protonation followed by deprotonation. 

Acid-catalysed hydration of conjugated diyncs is slower than that of simple alkynes, but still occurs under relatively mild conditions in the presence of sulphuric acid or especially sulphuric acid and mercury(ii) sulphate. Thus 2,3-butanedione (200) is obtained readily from butadiyne, without isolation of the intermediate monohydration product, 3-butyn-2-one (199). 

PROBLEM 9.14 Give the structure of the enol formed by hydration of 2-butyne, and write a series of equations showing its conversion to its corresponding ketone isomer. 

The vinylidene complexes 8 also react with nucleophiles such as water and methanol. Hydration of the unsubstituted vinylidene complex 8a leads to the formation of the rj -acetyl complex 13, whereas the corresponding reactions of 8b and 8c result in the C-C bond cleavage, giving the cationic carbonyl complex 14 and organocarbonyl products R COMe(R = OMe or Me). On the other hand, the reactions of 8 with methanol afford the methoxycarbene complex 15 and the vinyl complex 16, depending upon the substituent of the vinylidene complexes 8. Intramolecular nucleophilic attack takes place in the reaction of 4 with 3-butyn-l-ol, giving the cyclic alkoxycarbene complex [Cp RuCl(p-SPr%Ru =C(CH2)30 Cp ](OTf). ... 

CESIUM HYDRATE (21351-79-1) An extremely strong base. Violent reaction with acids, acetaldehyde, 2-butyne-l,4-diol, epichlorohydrin, glycidol. Incompatible with organic anhydrides, acrylates, alcohols, aldehydes, alkylene oxides, substituted allyls, cellulose nitrate, cresols, caprolactam solution, ethylene dichloride, isocyanates, ketones, glycols, nitrates, phenols, tyrothricin, vinyl acetate. Exothermic decomposition with maleic anhydride. Increases the explosive sensitivity of nitromethane. Attacks metals, including aluminum, copper, lead, tin, zinc. 

Mercury. A short account of the discovery of metal-catalyzed hydration of alkynes by Kucherov (1881) appeared on the occasion of its 125th anniversary [116]. Mercury-catalyzed hydration of alkynes has been used as mechanistic principle for devising fluorogenic probes for mercuric ions by two research teams. In one system, a 3-butyn-l-yl group at the phenolic oxygen of a fluorescein dye was cleaved via catalytic oxymercuration and elimination to releases a fluorescent dye (Scheme 20) [117]. In another system the mercury-catalyzed hydration of an ethynyl to an acetyl group provoked the quenching of fluorescence in a coumarine-based dye [118]. 

Dihydroxyacetone (44) was conveniently prepared from halogenopropargyl alcohol (43) by hydration of the triple bond followed by substitution of a halogen atom for the OH group in a reaction with potassium formate. DL-Erythrulose was obtained from 2-butyne-l,4-diol (45) in an improved way involving conversion to 1-acetoxy-3-buten-2-one (46), formation of the bromohydrin (47), substitution of the bromine atom for an OAc group in a reaction with silver acetate, and final deacetylation. 

The answer is C. When 1 -butyne is treated with sulfuric acid in the presence of mercuric oxide as catalyst, hydration occurs. The hydration follows Markovnikov s rule and forms a ketone. The reaction is given below ... 

For example, the mercuric-catalyzed hydration of 1-butyne gives l-buten-2-ol as an intermediate. In the acidic solution, the intermediate quickly equilibrates to its more stable keto tautomer, 2-butanone. 

In the experiment that follows, the hydration of a terminal alkyne is illustrated by the conversion of 2-methyl-3-butyn-2-ol (3) to 3-hydroxy-3-methyl-2-butanone (4), as shown in Equation 11.13. The presence of a hydroxyl group in 3 has little effect on the chemical properties of the carbontriple bond. Rather, the main effect of the polar hydroxyl group is on the physical properties of the molecule, with the boiling point of 3 being considerably higher than those of other acetylenic hydrocarbons having the same molecular weight. 

Analysis Determine the weight and percent yield of the distilled product. Determine the melting point of the semicarbazone of your product. Use this information to determine the identity of the product of hydration of 2-methyl-3-butyn-2-ol. The melting point of 6 is 162-163 °C, whereas 7 melts at 222-223 °C. Obtain IR and " H NMR spectra of your starting material and product and compare them with those of authentic samples (Figs. 11.3-11.6). 

Hydroxy-3-methyl-2-butanone (4) was produced by the hydration of 2-methyl-3-butyn-2-ol (3) in the experiment you performed. 

The procedures presented in this chapter represent basic reactions of alkynes. That involving hydration of 2-methyl-3-butyn-2-ol through electrophilic addition of water to the tr-system is a reaction analogous to the conversion of acetylene to acetaldehyde, a precursor to acetic acid and acetone. In addition, the formation of an alkyne via an elimination reaction illustrates an alternate approach to forming a carbon-carbon triple bond, although one that is not nearly so easy experimentally as adding water to calcium carbide to make acetylene ... 

FIGURE 7.6 The encapsulation of the NHC-Au(I) catalyst within the hexamer of resorcin[4] arene drastically changes the product distrihution in the terminal alkyne hydration of 4-phenyl-l-butyne. (Adapted from Ref. [30].)... 

Treatment of an alkenylborane with hydrogen peroxide in aqueous sodium hydroxide gives a product that corresponds to hydration of an alkyne that is, it corresponds to addition of H to one carbon of the triple bond and OH to the other as illustrated by the hydroboration-oxidation of 2-butyne. 

Problem 6.12. What are the products obtained on the mercury (Il)-catalyzed hydration of (a) ethyne (acetylene, HC=CH), (b) propyne (methylacetylene, CHjC CH), and (c) 2-butyne (dimethylacetylene, CHsC CCHs) Because ethyne (acetylene, HC=CH) and 2-butyne (dimethyl-acetylene, CHsC CCHs) are symmetrical, the carbon-carbon triple bond stretching frequency is IR inactive (Raman active) and... 

Give the products of mercuric ion-catalyzed hydration of (a) ethyne (b) propyne (c) 1-butyne (d) 2-butyne (e) 2-methyl-3-hexyne. 

Despite its own valuable synthetic potential, the use of [ C2]acetylene as a starting material for various building blocks is of much higher relevance. Mercury(II)-catalyzed hydration, for example, gives [ C2]acetaldehyde (Figure 8.5, Route 1) The same reaction carried out in the presence of ammonium persulfate furnishes [ 2] acetic acid (Route 2). Trapping of its mono- or dianion with formaldehyde or carbon dioxide affords [2,3- C2]propynol, [2,3- C2]butyne-l,4-diol, [2,3- C2]propiolic acid " and [2,3- C2]acetylenedicarboxylic acid, respectively (Routes 3-6). UV irradiation of a mixture of HBr and [ C2]acetylene produces l,2-dibromo[ C2]ethane (Route 8) . Reduction with chromium(II) chloride followed by a two-step epoxidation of the initially formed [ C2]ethylene converts [ 2]acetylene into [ C2]ethylene oxide (Route 7) . Finally, catalytic homotrimerization or co-trimerization with other alkynes provides [ " C ]benzene or substituted [ " C ]benzenes, respectively, the central starting materials for the vast majority of substituted benzenoid aromatic compounds (Route 9). 

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