Alkaline process

In the alkaline process, an aqueous solution of sodium hydroxide is allowed to react with molten, yellow phosphoms. A long-chain alcohol is used as a dispersant (3). The reaction to produce phosphine may be represented by equation 1. 

The acid process has three advantages over the alkaline process, ie, (/) higher yield of phosphine (60 vs 25%) (2) more pure gas for use in subsequent reactions (95 vs 40%) and (J) by-product phosphoric acid is relatively valuable and can be sold into a number of markets, eg, in the manufacture of fertilizers and flame retardants. There is no ready outlet for the mixture of phosphites produced via the alkaline route and additional processing by oxidative spray drying is needed to produce phosphates for sale (3). 

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). 

No toxicological hazards have been associated with the normal use of instant color films. However, direct contact with the highly alkaline processing fluids can cause alkafl bums. The fluids are provided in sealed pods and are not usually handled by the user. In the integral systems, the fluids are retained within the film unit and neutralized in the course of processing. In the peel-apart films, residual fluids are rapidly rendered harmless by contact with the air. 

Cleaners containing silicate can cause problems. They should not be used prior to an alkaline process on aluminium, owing to the formation on the surface of alkali-insoluble aluminium silicate. Silicated cleaners can also cause problems before some surface-sensitive zinc phosphating solutions, especially the more modern low-zinc type. 

Recycling of some, mainly alkaline process water from the bleach plant... 

Phosphonates are useful additions in acidification treatments after alkaline processing to assist in the removal of metal compounds that have limited solubility in alkali. 

Although acidic pulping methods have largely been displaced over the past 50 years by neutral and alkaline processes, there is still a significant amount carried out. Acid sulfite pulping uses combinations of sulfur dioxide and water at high temperatures and pressures. An appropriate base is used to control the pH and, although usually acidic, it is possible to perform these reactions at neutral or even alkaline pH. The most active nucleophile present is the bisulfite ion,... 

The biological uptake of N03, on the other hand, is an alkalinizing process (i.e., uptake of N03 consumes 1 mole of H per mole of N assimilated). 

In the alkaline process, uranyl carbonate is eluted from the resin by concentrated (approximately 1 M) solutions of chloride, carbonate or bicarbonate, and is recovered from the eluate by treatment with an acid to destroy the carbonate complex, followed by precipitation of the diuranate, e.g. 

A limited set of phenylenediamine color developers are used. Kodak s CD-3, CD-4, and CD-6 (26-28) are the principle color developers used today [31], They are directly incorporated into the alkaline processing fluid. The methyl group in the 2-position is important for preventing side reactions and enhancing the formation of the desired dye. The phenylenediamine undergoes a two-electron oxidation to quinonediimine, which then reacts with the color couplers to form the desired chromophores [32],... 

Continuing with the pH trend, peroxide solutions are readily decomposed in alkaline solution, whereas near-neutral decomposition processes rely heavily on catalytic activity of the decomposition agent, alkaline processes relying more on the inherent instability of the perhydroxyl anion under high pH conditions. 

Provansal, M.M.P., Cuq, J.-L.A. and Cheftel, J.-C. (1975). Chemical and nutritional modifications of sunflower proteins due to alkaline processing. Formation of amino acid crosslinks and isomerization of lysine residues. J. Aqric. Pood Chem. 23, 938-943. 

---