Resorcinol, hydrogenation

Our task was to develop a feasible synthesis for diamino resorcinol. From several possibilities [1-4] the resorcinol and anihne were chosen as starting materials. The diazotated aniline was coupled with resorcinol among basic conditions giving 4,6-bisphenylazo resorcinol. Hydrogenation of the latter resulted in diamino resorcinol and aniline, which could be recycled (scheme 14.2). This chemistry is well known [5-13] therefore, the research work focused on finding the optimal parameters and catalyst and finally on elaborating a process for scale-up. 

Pyridylazo)resorcinol 4-(2-Pyridylazo)resorcinol + Tetradecyldimethyl-benzylammonium chloride 4-(2-Pyridylazo)resorcinol + Hydrogen peroxide Cobalt Nitroso-R salt... 

Ca.ta.lysis by Protons. The discovery of hydrogen peroxide hydroxylation of phenol in the presence of strong acids such as perchloric, trifluoromethane-sulfonic, or sulfuric acids allows suppression of all previous drawbacks of the process (18,19). This mode of hydroxylation gives high yields (85% based on H2O2 at phenol conversion of 5—6%). It can be mn without solvents and does not generate resorcinol. Its main advantage rehes on... 

The synthesis of 2,4-dihydroxyacetophenone [89-84-9] (21) by acylation reactions of resorcinol has been extensively studied. The reaction is performed using acetic anhydride (104), acetyl chloride (105), or acetic acid (106). The esterification of resorcinol by acetic anhydride followed by the isomerization of the diacetate intermediate has also been described in the presence of zinc chloride (107). Alkylation of resorcinol can be carried out using ethers (108), olefins (109), or alcohols (110). The catalysts which are generally used include sulfuric acid, phosphoric and polyphosphoric acids, acidic resins, or aluminum and iron derivatives. 2-Chlororesorcinol [6201-65-1] (22) is obtained by a sulfonation—chloration—desulfonation technique (111). 1,2,4-Trihydroxybenzene [533-73-3] (23) is obtained by hydroxylation of resorcinol using hydrogen peroxide (112) or peracids (113). 

Hydroquinone [123-31 -9] represents a class of commercially important black-and-white chemical reducing agents (see Hydroquinone,RESORCINOL, AND catechol). The following scheme for silver haUde development with hydroquinone shows the quantitative importance of hydrogen ion and haUde ion concentrations on the two half-ceU reactions that describe the silver—hydroquinone redox system ... 

A solution of resorcinol (11 g) in sodium hydroxide solution (4.8 g of sodium hydroxide in 20 ml of water) is hydrogenated in the presence of 1.1 g of 5 % rhodium on alumina for 16-18 hours at 50 psi initial pressure in a Parr apparatus. The reduction stops after the absorption of 1 equivalent of hydrogen. The catalyst is removed by filtration through celite, and the aqueous solution is carefully acidified with concentrated hydrochloric acid at 0°. The crude product is collected by filtration, dried in air, and recrystallized from benzene to give 1,3-cyclohexanedione, mp 105-107. ... 

Palladium may not be preferred for dihydric aromatics. Dihydroresorcinol was obtained in 87% yield by alkaline hydrogenation of resorcinol over 5% Rh-on-C (65) and in only 50-60% yield over Pd-on-C 15). A 77% yield of the dione was obtained by alkaline hydrogenation of 3,5-dihydroxyphenylacetic acid over a 10% loading of 5% Rh-on-AljOj at 55"C and 55 psig (39a). 

Elsewhere, in a series of Japanese patents, mixtures of resorcinol + sodium nitrate, glycerine + sodium nitrate, lithium hydroxide + tungstate, etc., have been claimed to be effective. An example of the use of inhibited cooling mixtures of low toxicity is provided by a patent which describes a mixture of silicate-I- polyphosphate -I- a saccharide, e.g. sucrose or fructose, as the inhibitor formulation in a propylene glycol -I- potassium-hydrogen-carbonate mixture used in aluminium cooler boxes for ice-cream. 

Hydrogenation, of gallic add with rhodium-alumina catalyst, 43, 62 of resorcinol to dihydroresorcinol, 41,56 Hydrogen peroxide, and formic acid, with indene, 41, 53 in oxidation of benzoic add to peroxy-benzoic add, 43, 93 in oxidation of ieri-butyl alcohol to a,a/r, a -tetramcthyltetra-methylene glycol, 40, 90 in oxidation of teri-butylamine to a,<, a, a -tetramethyltetra-methylenediamine, 40, 92 in oxidation of Crystal Violet, 41, 2, 3—4... 

Neopentyl alcohol, 40, 76 Nickel catalyst for hydrogenation of resorcinol, 41, 56, 57 Nitramines from amines and acetone cyanohydrin nitrate, 43, 84 Nitration, of amines to nitramines by acetone cyanohydrin nitrate, 43, 83... 

It is a lipophilic compound which removes intercellular lipids that are covalently linked to the cornified envelope surrounding epithelial cells [3]. It also enhances penetration of other agents. Resorcinol (m-dihydroxy benzene) is structurally and chemically similar to phenol. It disrupts the weak hydrogen bonds of keratin [4]. Lactic acid is an alpha hydroxy acid which causes corneocyte detachment and subsequent desquamation of the stratum corneum [5]. 

A hydrogenation process for the preparation of 4,6-diamino resorcinol from 4,6-bisphenylazo resorcinol was studied and developed up to pilot scale. The high reaction rate together with the protection of the product against oxidation could ensure providing the addition of HCl was made after the fast hydrogenation period. Activity and lifetime of commercial catalysts were evaluated also. 

The substrate, catalyst and solvent were placed into a glass liner equipped with a magnetic stir bar. The liner was placed in a 250 mL steel autoclave that was then charged at r.t. first with N2, then with H2. The reaction mixture was stirred at r.t. until the hydrogen consumption ceased, after which the H2 was vented, the autoclave flushed with N2 and the reaction mixture filtered off on glass filter. The solution was evaporated and the products crystallized and filtered. The crystalline mixture contained the hydrochloride salt of diamino resorcinol and aniline In order to separate completely diamino resorcinol and aniline, the product mixture has to be recrystallized from hydrochloric acid solution. 

Already after the first preliminary hydrogenation experiments, it became evident that diamino resorcinol carmot be manipulated in its base form, as contacting with traces of air it is oxidized, which appears in changing its pink color during seconds to daik purple. 

Avoiding the fast oxidation acidic medium was applied, the hydrogenation was carried out in methanol-water mixture containing a stoichiometric amount of hydrochloric acid, 4 mole with respect to 1 mole 4,6-bisphenylazo resorcinol. Under... 

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