Carboxylation of resorcinols

Mechoulam R, Ben-Zvi Z, Carboxylation of resorcinols with methyl magnesium carbonate. Synthesis of cannabinoid acids, Chem Commun 343—344, 1969. 

The nmr chemical shifts of alkah metal ( K, Na etc.) phenoxide moved to down field upon formation of the complex, [ phenoxide-M CO2] with carbon dioxide in the Kolbe-Schmitt reaction. The complex formed under pressure of carbon dioxide showed more increments in weights and chemical shifts, as much as 0.72 ppm of (5 paia of potassium phenoxide at 5 MPa. The kinetic studies on the carboxylation of resorcinol in aqueous hydrogencarbonates with carbon dioxide revealed an equilibrium between resorcinol and the product or resorcylic acid. 

The Kolbe-Schmitt reaction[l] has long history related with aspirin and has been a name reaction used for the longest period in an industrial process. While the demand for the manufacturing aromatic hydroxycarboxyhc acids is still successively coming out today with a number of patents, the mechanism of the reaction has remained unsolved. The present nmr spectroscopic studies have proved a [substrate CO2] complex or an intermediate prior to the formation of carboxyhc acids. Another puzzling question about the unstable complex even to moisture, is why the carboxylation of polyhydroxybenzenes, such as resorcinol, should proceed in aqueous solutions. Herein also reported are kinetic studies on the carboxylation of resorcinol in aqueous solutions of alkali hydrogencarbonates. 

The Kolbe-Schmitt reactions of polyhydroxy phenols such as resorcinol, pyrogallol and phloroglucinol are exceptionally carried out in aqueous solution.[6] Any explanation has not yet been given to the reason of the exception. Kinetic studies on the carboxylation of resorcinol (ROH) with hydrogencarbonate (KHCO-O were carried out in aqueous solutions. 

The ki of the carboxylation of resorcinol with ammonium hydrogencarbonate was about one tenth of that with potassium hydrogencarbonate. These results are in agreement with the reported lower yield (53.9%) [7] of the product even at applying higher pressure (5 MPa) and higher temperatures (110-125 °C). 

Carboxylation of resorcinols. The acidity of the aromatic hydrogens in resorcinols prompted Israeli chemists4 to investigate the possibility of carboxylation with magnesium methyl carbonate. The reaction was successful. Thus resorcinol gave /3-resorcylic acid (45%) and 2,4-dihydroxyisophthalic acid (15%), together with starting material (43%). 

Resorcinol carboxylation with carbon dioxide leads to a mixture of 2,4-dihydroxyben2oic acid [89-86-1] (26) and 2,6-dihydroxyben2oic acid [303-07-1] (27) (116). The condensation of resorcinol with chloroform under basic conditions, in the presence of cyclodextrins, leads exclusively to 2,4-dihydroxyben2aldehyde [95-01-2] (28) (117). Finally, the synthesis of l,3-bis(2-hydroxyethoxy)ben2ene [102-40-9] (29) has been described with ethylene glycol carbonate in basic medium (118), in the presence of phosphines (119). Ethylene oxide, instead of ethyl glycol carbonate, can also be used (120). 

The carboxylation reaction is particularly facile with di- and tri-hydric phenols. Thus 2,4-dihydroxybenzoic acid (Expt 6.156) is readily obtained by passing carbon dioxide through a boiling aqueous solution of the potassium or sodium salt of resorcinol. 

Dihydroresorcinol has been prepared by the reduction of resorcinol with sodium amalgam,2 by reduction of hydroxyhydroqui-none or its carboxylic acid with sodium amalgam,3 by hydrolysis of its dioxime,4 or by cyclization of ethyl y-acetylbutyrate.s The present method of preparation is essentially that of Klingenfuss.6... 

Oxygen has been identified in carboxylic, phenolic, and ketonic locations (55, 56, 63-65) but is not usually regarded as being located primarily in heteroaromatic ring systems. In the context of polyhydroxy aromatic nuclei, it is of interest to note that pyrolysis of asphaltenes at 800 °C results in the formation of resorcinol (63), implying that such functions may indeed exist in the native material. 

The facile decarboxylation of resorcinol carboxylic acids and notably of orsellinic acids in alkaline solution poses a problem during their syntheses in high yield. For this reason the synthesis of alkoxycarbonyl derivatives is usually adopted followed by acidic hydrolysis. The removal of the protective acetyl groups in the compound shown was effected preferentially without hydrolysis of the ester group. Methyl 2,6-diacetoxybenzoate in toluene saturated with water when add to a catalyst (prepared from 4-toluenesulphonic acid monohydrate and silica gel) and stirr at 86°C during 6 hours, afford methyl... 

Christman et al. (1978) also chlorinated resorcinol, showing that during chloroform formation it underwent ring contraction to produce the unusual cyclopentene-dione 25. Larson and Rockwell (1979) confirmed Rook s and Christman s observations that resorcinol derivatives were active haloform precursors, and also found that even if the 2-carbon of resorcinol was blocked by a carboxyl group (cf. 26), yields of... 

Further proof of complex reactions between propylene carbonate and phenolic nuclei leading to compounds in which the carbonic acid has attacked the phenolic ring has been presented [23] based on the NMR spectrum of the product of the reaction of resorcinol with propylene carbonate, in the absence of formaldehyde. Resorcinol was chosen as its aromatic ring is a stronger nucleophile than that of phenol and thus if any reaction had occurred this would be less elusive and much more easily observed [23]. The reaction products which appeared to be formed were carboxylic and dicarboxylic species. That they might be present was also derived by NMR [23]. It must be pointed out that such structures need to be only transitory and not permanent to obtain the same effects noted experimentally. Such a subsequent lability could be the reason why it is difficult to observe such linkages in the hardened resin except for faster reacting phenols where they can be observed due to early immobilization of the network which surely occurs. 

Formylations of phenol, resorcinol and indole, dichloromethylations of 4-methylphenol and 5,6,7,8-tetrahydro-2-naphthol, carboxylation of phenol, and allylation of 2,4,6-trimethylphenol proceed site-selec-tively in high yields by using 3-cyclodextrin as catalyst. The formation of ternary inclusion complex composed of cyclodextrin, substrate, and dichlorocarbene, trichloromethyl cation or allyl cation in the reaction mixture is an important factor of the site-selective reactions. The cyclodextrin is also effective by limiting the molecular size of the reaction intermediate. 

As regards organic contaminants, leachates from semi-coke contain compounds such as phenols, for example, cresols, resorcinols, and xylenols, which occur at mg/L concentrations. Indeed, Kahru et al. (2002) found total phenols at concentrations up to 380 mg/L in semi-coke dump leachates. Phenols also volatilize from such leachates, depending on temperature and pH (Kundel Liblik 2000). Atmospheric phenol concentrations of 4-50 xg/m3 have been observed in the proximity of leachate ponds (Koel 1999). Generally, aliphatic hydrocarbons, carboxylic acids, and organo-nitro and organo-sulpho compounds do not occur at elevated concentrations in leachates from Estonian semi-coke (Koel 1999). 

The use of triethyl orthobut-2-ynoate, MeC=CC(OEt)3, yields 4-methylcoumarins, whilst with dimethyl butynedioate, resorcinol affords methyl coumarin-4-carboxylate in a reaction catalyzed by zinc chloride (69MI22400). The potential elaboration of this approach to coumarins is quite apparent. 

Exercise 26-7 1,3-Benzenediol (resorcinol) can be converted to a carboxylic acid with carbon dioxide and alkali. Would you expect 1,3-benzenediol to react more, or less, readily than benzenol Why Which is the most likely point of monosubstitution Explain. 

These compounds can condense and cyclize with resorcinol or substituted 3-aminophenols. Nucleophilic substitution of chlorine by amines leads to xanthene dyes which contain a sulfonic acid group [10] or hydrogen [11] instead of the carboxyl group. 

First, 1 2 metal complexes of (mainly mono-) azo dyes, without sulfonic or carboxylic acid groups, and trivalent metals (see Section 3.11). The metals are preferably chromium and cobalt nickel, manganese, iron, or aluminum are of lesser importance. Diazo components are mainly chloro- and nitroaminophenols or amino-phenol sulfonamides coupling components are (3-naphthol, resorcinol, and 1-phe-nyl-3-methyl-5-pyrazolone. Formation of a complex from an azo dye and a metal salt generally takes place in the presence of organic solvents, such as alcohols, pyridine, or formamide. An example is C.I. Solvent Red 8, 12715 [33270-70-1] (1). 

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