Carbonate developing agents

Developing agents must also be soluble in the aqueous alkaline processing solutions. Typically such solutions are maintained at about pH 10 by the presence of a carbonate buffer. Other buffers used include borate and, less frequendy, phosphate. Developer solubiUty can be enhanced by the presence of hydroxyl or sulfonamide groups, usually in the A/-alkyl substituent. The solubilization also serves to reduce developer allergenicity by reducing partitioning into the lipophilic phase of the skin (46). 

Sodium bisulfite is often preferred in pyro developers and in Phenidone concentrates (Appendix 3 Pharmacopoeia Phenidone). Sodium bisulfite3 is often used in formulas that are divided into two solutions, as its weak acidity helps to inhibit the oxidation of the concentrated developing agent. When carbonate, contained in the B solution, is added to make a working solution, the bisulfite is immediately broken down into sulfite and bicarbonate, producing a useful buffering effect. 

Technique of Divided Development In divided development, two separate baths are used. The first bath contains the developing agent(s), restrainer, and preservative. The second bath contains the accelerator. The second bath is used to activate the developer. Borax is the least active accelerator metaborate is about double the strength of borax carbonate is about double the strength of metaborate. Hydroxide is the most active of the alkalis and the least controllable. 

Uses As a developing agent used in conjunction with sodium or potassium carbonates or with caustic alkali. The sodium salt of this is the developing agent in the concentrated solution of prepared developer. It is marketed under the trade name of Rodinal by Agfa. 

Inhibitors to the enzyme carbonic anhydrase. This enzyme is widely distributed in the body and has a fundamental role in the control of acid-base balance. In the 1920s it was noticed that the SULPHONAMIDE sulfanilamide had a weak diuretic action. Acetazolamide is a subsequent thiadiazole-sulphonamide derivative with potent carbonic anhydrase inhibitor activity. Clinically, it is used for antiglaucoma TREATMENT, is a weak diuretic and can be used to treat mountain sickness. Dichlorphenamide and dorzolamide are sulphonamide derivatives also used for antiglaucoma treatment. Methazolamide is used as a diuretic. Now that seven or more isoenzymes of carbonic anhydrase have been cloned. Isolated and mapped, some new initiatives are aimed at developing agents with more selective actions. 

The oxidation of the compounds used as developers is accelerated in the presence of alkalies and retarded by acids for this reason most developers are made up just before use from two solutions, one containing the developing agent, and the other sodium carbonate. 

Preparation by Nucleophilic Addition.- The monoanion of 1, 4-dioxene has been developed as a two-carbon homologating agent for converting carbonyl compounds into B-keto-alcohols via an addition-... 

The earhest frothing process developed was the Dunlop process, which made use of chemical gelling agents, eg, sodium fluorosiUcate, to coagulate the mbber particles and deactivate the soaps. The Talalay process, developed later, employs freeze-coagulation of the mbber followed by deactivation of the soaps with carbon dioxide. The basic processes and a multitude of improvements are discussed extensively in Reference 3. A discussion more oriented to current use of these processes is given in Reference 115. 

One-part urethane sealants (Table 3) are more compHcated to formulate on account of an undesirable side reaction between the prepolymer s isocyanate end and water vapor which generates carbon dioxide. If this occurs, the sealant may develop voids or bubbles. One way to avoid this reaction is to block the isocyanate end with phenol and use a diketamine to initiate cure. Once exposed to moisture, the diketamine forms a diamine and a ketone. The diamine reacts with the isocyanate end on the prepolymer, creating a cross-link (10). Other blocking agents, such as ethyl malonate, are also used (11). Catalysts commonly used in urethane formulations are tin carboxylates and bismuth salts. Mercury salt catalysts were popular in early formulations, but have been replaced by tin and bismuth compounds. 

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