Bromide to chloride

Chlorobromide papers are the most commonly used today. As the name implies, they are a compromise between the fast bromide and the slow chloride papers. Chlorobromide papers are usually slower than bromides. The percentage of bromide to chloride can allow manufacturers to create either warm- or cold-toned papers with a variety of sensitivities. Examples of chlorobromide papers include Ilford MG IV and Warmtone , Kentmere Kentona , Fomatone MG Classic VC , Slavich Bromportrait , and Fotokemika Emaks . 

This is consistent with the conclusion that the amount of loose radical pair formed is determined by the strength of the carbon-halogen bond. As the halogen is changed from iodide, to bromide, to chloride, the bond strength increases and more energy is required to add an additional electron to the carbon-halogen bond. Consequently, the lifetime of the intermediate radical ion decreases in this order, and the reaction becomes more concerted, with the consequence that there is less loose radical pair formed and, thus, less racemization and loss of material to side processes. 

In general, the ease of synthesis of alkyl halides from olefins is dependent on the molecular weights of the hydrocarbons and the particular hydrogen halide. Thus, as was explained earlier in this chapter, the reaction becomes more difficult in passing from iodides through bromides to chlorides. Likewise, olefins containing several carbon atoms react much more readily than those of a lower order. 

In 45 experiments involving three dogs in which the plasma bromide concentration ranged from 0.011 to 0.048 mN, I found that bromide exactly replaces chloride in plasma their sum is constant. The ratio of bromide to chloride in gastric juice exceeded the ratio in plasma, but it fell off as the bromide concentration increased (Fig. 1-13). The stomach seems to prefer to secrete bromide slightly more than chloride, but this preference decreases as the bromide concentration increases. 

Figure 1-13. Left Ordinates, mobilities of bromide in water (top) obtained from Lan-dolt-Bornstein s Physikalische-Chemie Tabellen, plotted against molarity as abscissae. Below, the same for chloride. Right a, the ratio of mobilities of bromide to chloride plotted against the ratio of the concentrations of the two ions in plasma b, the secretion constant according to equation (1-2) plotted against the ratio of the two ions in plasma. (From Davenport HW, Fisher RB. The mechanism of the secretion of acid by the gastric mucosa. Am I Physiol 131 165-175, 1940.)...

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