Hydration of triple bonds

The hydration of triple bonds is generally carried out with mercuric ion salts (often the sulfate or acetate) as catalysts. Mercuric oxide in the presence of an acid is also a common reagent. Since the addition follows Markovnikov s rule, only acetylene gives an aldehyde. All other triple-bond compounds give ketones (for a method of reversing the orientation for terminal alkynes, see 15-16). With allqmes of the form RC=CH methyl ketones are formed almost exclusively, but with RC=CR both possible products are usually obtained. The reaction can be conveniently carried out with a catalyst prepared by impregnating mercuric oxide onto Nafion-H (a superacidic perfluorinated resinsulfonic acid). ... 

Despite the high temperatures which are used in these reactions, our results show that zeolites are effective catalysts for promoting hydration of triple bond derivatives in respect of an easy handling and avoidance of corrosion. 

It is remarkable that the mechanistic parameters, rates included, for the acid-catalyzed hydration of compounds (2) and (3), are in general, similar to those observed in the reaction of the corresponding alkenes. This has been illustrated in detail by Richey and Richey (1970) and will be discussed in section IIIA2a. The hydration of triple bonds may be faster than that of double bonds, as shown by the main product obtained from the alkynyl alkenyl ether under 9 of Table 1. 

The lack of regiocontrol during the hydration of triple bonds in substituted but-2-yne-l,4-diols has meant that they are not especially useful for the construc-... 

Conjugated dienes can be selectively hydrated to ketones in the presence of cationic ruthenium complexes with bipyridyl ligands. The role of ruthenium is to catalyze the isomerization of allylic alcohols formed by the addition of water to diene. This method allows one to convert butadiene to methyl ethyl ketone in high yield [187]. Hydration of triple bonds is one of the oldest catalytic processes of organic chemistry. Though this reaction has no industrial value, it can serve as a tool of fine organic synthesis. The hydration can be catalyzed by rhodium salts under phase-transfer conditions [188]. The more exotic process of the hydrolysis of phenylacetylene to toluene and carbon monoxide catalyzed by ruthenium complex should also be mentioned [189] ... 

K. Tani and Y. Kataoka, begin their discussion with an overview about the synthesis and isolation of such species. Many of them contain Ru, Os, Rh, Ir, Pd, or Pt and complexes with these metals appear also to be the most active catalysts. Their stoichiometric reactions, as well as the progress made in catalytic hydrations, hydroal-coxylations, and hydrocarboxylations of triple bond systems, i.e. nitriles and alkynes, is reviewed. However, as in catalytic hydroaminations the holy grail", the addition of O-H bonds across non-activated C=C double bonds under mild conditions has not been achieved yet. 

In both cases, the hydration reaction of triple bonds over zeolites has received little attention. 

It is often difficult to induce selective addition to double bonds in the presence of triple bonds because of the reactivity of the latter. Dicobalt octa-carbonyl selectively adds to a triple bond in the presence of a double bond and allows selective transformation of the non-co-ordinated olefinic bond. Removal of the protecting metal is simple. Thus vinylacetylenes when treated with strong acids usually form the products of hydration of the triple bond, and the ene-yne-ol (140) reacts with fluoroboric-acetic acid at 25 C for 24 h to form an intractable mixture. Its complex (141) reacted at 0 °C for 15 min to give 91 % of (142) on work-up, which implies a metal-stabilized carbonium ion intermediate. Oxidative degradation with Fe(N03)3 generates the acetylene (143) in excellent yield. 

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. 

The addition of acetylides to oxiranes yields 3-alkyn-l-ols (F. Sondheimer, 1950 M.A. Adams, 1979 R.M. Carlson, 1974, 1975 K. Mori, 1976). The acetylene dianion and two a -synthons can also be used. 1,4-Diols with a carbon triple bond in between are formed from two carbonyl compounds (V. Jager, 1977, see p. 52). The triple bond can be either converted to a CIS- or frans-configurated double bond (M.A. Adams, 1979) or be hydrated to give a ketone (see pp. 52, 57, 131). 

C = C triple bonds are hydrated to yield carbonyl groups in the presence of mercury (II) ions (see pp. 52, 57) or by successive treatment with boranes and H2O2. The first procedure gives preferentially the most highly substituted ketone, the latter the complementary compound with high selectivity (T.W. Gibson, 1969). 

Acid catalyzed hydration (Section 9 12) Water adds to the triple bond of alkynes to yield ketones by way of an unstable enol intermediate The enol arises by Markovnikov hydration of the alkyne Enol formation is followed by rapid isomerization of the enol to a ketone... 

Hydration. Water adds to the triple bond to yield acetaldehyde via the formation of the unstable enol (see Acetaldehyde). The reaction has been carried out on a commercial scale using a solution process with HgS04/H2S04 catalyst (27,28). The vapor-phase reaction has been reported at... 

The initial reaction is probably the acid-catalyzed hydration of the triple bond, followed by dehydration of the 17-hydroxyl group... 

Hydration of alkynes (Section 9.12) Reaction occurs by way of an enol intermediate formed by Markovnikov addition of water to the triple bond. 

The hydration of 5-amino-3-cyano-l-(2,6-dichloro-4-trifluoromethylphenyl)-4-ethynylpyrazole was performed with p-toluenesulfonic acid monohydrate in acetonitrile (2 h, room temperature) to give the corresponding 4-acetyl derivative. An alkyl substituent at the triple bond decreases the rate of hydration the conversion of 5-amino-3-cyano-l-(2,6-dichloro-4-trifiuoromethylphenyl)-4-(prop-l-yn-l-yl) pyrazole to the 4-propanoylpyrazole was completed after 18 h (98INP9804530 99EUP933363). 

The reaction of disubstituted diacetylenes with hydrazine hydrate was reported by Darbinyan et al. (70AKZ640). In the first stage the addition of hydrazine to the terminal carbon atom of the diacetylene system is analogous to that of primary amines to diacetylene (69ZC108 69ZC110). With monosubstituted diacetylenes (R = H), hydrazine adds to the terminal triple bond. This leads to the formation of vinylacetylenic hydrazine 22 which cyclizes to dihydropyrazole 23 subjected to further isomerization to the pyrazole 25. It is possible that hydrazine 22 undergoes hydration to the ketone 24 which can easily be cyclized to the pyrazole 25... 

AKZ640). Although some data (00UK642) support a ready hydration of the activated triple bond in a weakly basic medium, the latter route seems less probable, since the cyclization of hydrazine 22 is a monomolecular process (70AKZ640) and the hydrazine group is much more nucleophilic than water. 

The hydrolysis of l-alkoxybut-l-en-3-ynes in the presence of acids can follow two directions (a) hydration of the triple bond and (b) hydrolysis of the vinyl ether structural element to form propiolic aldehyde 138 (55CB361). 

Add hydrolysis of l-ethylthiobut-l-en-3-yne (143) (10% sulfuric acid, 60-95°C) mainly involves hydration of the triple bond (evidently due to the greater hydrolytie stability of the vinyl sulfide moiety of the moleeule), whieh results in the formation of l-ethylthiobut-l-en-3-one (144). The latter is further hydrolyzed to aeetoaeetie aldehyde (132) (75IZV1975 78IZV153). 

As the data in Table 1 indicate, there is a strong dependence of the hydration on the electron demands of the substituents, with a rho of -4.3 in the Yukawa-Tsuno (18) equation, where logk is plotted against p[a + t a — a)]. Partial hydration of CsHsC CT and recovery of the unreacted starting material did not result in any loss of specific activity, which indicates that the protonation of the triple bond is not significantly reversible and hence is rate determining. 

The degradation of alkynes has been the subject of sporadic interest during many years, and the pathway has been clearly delineated. It is quite distinct from those used for alkanes and alkenes, and is a reflection of the enhanced nucleophilic character of the alkyne C C bond. The initial step is hydration of the triple bond followed by ketonization of the initially formed enol. This reaction operates during the degradation of acetylene itself (de Bont and Peck 1980), acetylene carboxylic acids (Yamada and Jakoby 1959), and more complex alkynes (Figure 7.18) (Van den Tweel and de Bont 1985). It is also appropriate to note that the degradation of acetylene by anaerobic bacteria proceeds by the same pathway (Schink 1985b). 

Abstract The use of A-heterocyclic carbene (NHC) complexes as homogeneous catalysts in addition reactions across carbon-carbon double and triple bonds and carbon-heteroatom double bonds is described. The discussion is focused on the description of the catalytic systems, their current mechanistic understanding and occasionally the relevant organometallic chemistry. The reaction types covered include hydrogenation, transfer hydrogenation, hydrosilylation, hydroboration and diboration, hydroamination, hydrothiolation, hydration, hydroarylation, allylic substitution, addition, chloroesterification and chloroacylation. 

The hydration of C-C triple bonds represents one of the most atom economical and environmentally friendly oxidation reactions [37], Recently, Nolan and co-workers reported the cationic [Au(lPr)][SbF ] system, which was generated in situ from [AuCl(lPr)] and AgSbF. The catalyst system showed remarkable activity in the hydration of a large range of alkynes, at An loadings as low as 10 ppm (typically 50-100 ppm), under acid-free conditions (Table 10.6) [38],... 

To understand what we have just said, let us consider the following example a ketone can be obtained by hydration of a triple bond. If the triple bond is a terminal one, the ketone that will form does not pose any doubt however, if the triple bond is in the middle of a carbon chain there is a question of regioselectivity, since the ketone can be formed in two different positions. The transform corresponding to this reaction can be represented with the following scheme ... 

---