Re-acidification

The reactivity of these tricyclic compounds has been investigated in detail. Reaction of these with sodium cyanoborohydride in acetic acid reduces the imine double bonds to give the tetrahydro-derivatives, for example, 37 gives 39. Reaction of 37 with sodium methoxide results in the ring-opened sulfonate salt 40 re-acidification of this salt gives the corresponding sulfonic acid which cyclizes back to the tricycle 37. Further heating of the sulfonic acid... 

These new fermentation processes often require high costs for recovering the product from the fermentation broth. For instance, the production of lactic acid requires the neutralization of the product during the fermentation, to avoid acidification of the medium, and the subsequent re-acidification of the lactate [65]. Similarly, the recovery of 1-butanol implies the distillation of large amounts of water. Alternative recovery processes are therefore the subject of intensive research. 

Yeast showed an accumulation of PolyP3 following PolyP hydrolysis induced by amines and basic amino acids (Greenfeld et al., 1987). The degradation of NMR-observable , probably vacuolar, PolyP to short-chain polymers in the cells of Chemostat-cultivated S. cerevisiae contributed to neutralizing the added alkalinity (Castro et al., 1995, 1999). In contrast, when the vacuolar vphl-1 mutant, lacking NMR-visible PolyP, was subjected to alkalinization, the absence of a vacuolar source of phosphate slowed re-acidification (Castro et al., 1999). Anaerobiosis resulted in the complete hydrolysis of PolyP to P (Castro etal, 1995). 

If the nitric acid solution is boiled, then treated with KI, it turns a muddy red-brown color. Treatment of this muddy solution with Na2S203 discharges much of the color, leaving a finely divided red precipitate, identical to solid D. Solution B is boiled, then treated with a small amount of HgCl2. A white precipitate forms, then slowly turns black, (E). The filtrate from E is treated with H2S, yielding a yellow precipitate, F, which is soluble in concentrated NaOH but is reprecipitated upon re-acidification. 

Oxidation in acidic solution can be achieved by Caro s acid, for example at 85 °C.247 This chemistry is employed in the extraction of chromium from superalloy scrap.248 It can also be used to detoxify, recover or re-cycle effluents from chromic acid oxidation or pickling liquors. Detoxification and recovery of chromic acid solutions is by the addition of hydrogen peroxide which reduces the chromium(III) salts, followed by alkali to precipitate and separate chromium hydroxide.249 Re-cycle can be by direct re-oxidation with Caro s acid, or by first raising the pH to alkaline levels, oxidation with hydrogen peroxide and re-acidification with subsequent salt by-product production. 

Need for water re-acidification in order to comply with discharge guidelines... 

A variety of protocols utilising combinations of liquid-liquid and solid-phase extractions (LLE and SPE) have been used to clean-up tissue extracts. Alkaline extracts are commonly made acidic, extracted into ethyl acetate and then back-extracted into aqueous buffer at alkaline pH. Acidic extracts have been extracted directly into ethyl acetate and then back-extracted into buffer. QCA and mQCA may act as acids or bases, and both of these properties have been utilized in the SPE clean-up of the buffered extracts from the initial liquid-liquid partitions. Extracts were acidified prior to clean-up on non-endcapped sex (strong cation exchange) SPE columns. The analytes of interest were eluted from the columns using a mixture of sodium hydroxide and methanol. Further clean-up and transfer to an appropriate solution for instmmental analysis was achieved by re-acidification... 

The decomposition of the conjugate acid of the intermediate is dependent on the acidity of the medium product. Studies have shown that after the initial reaction has been allowed to take place, re-acidification in the presence of a trace of catalyst yields a mixture of (9) with some 25 % of (8) even though the spectrum of (8) had been destroyed by the initial addition of base, whereas in basic media only the product (9) is generated ... 

The following are examples of the above procedure. A mixture of diethylamine and re-butyl alcohol may be separated by adding sufficient dilute sulphuric acid to neutralise the base steam distillation will remove the alcohol. The amine can be recovered by adding sodium hydroxide to the residue and repeating the distillation. A mixture of diethyl ketone and acetic acid may be treated with sufficient dilute sodium hydroxide solution to transform the acid into sodium acetate and distilling the aqueous mixture. The ketone will pass over in the steam and the non-volatile, stable salt will remain in the flask. Acidification with dilute sulphuric acid hberates acetic acid, which can be isolated by steam distillation or by extraction. 

Heteratisine, C22H33O5N, crystallises in prisms, has m.p. 262-7° (dec.), [a]f7° + 40° (MeOH), forms a hydrochloride, m.p. 265-270° (dec.), contains one methoxyl and one methylimino group, two active hydrogens and a lactone ring, opened by alkali and re-formed on acidification. In a later paper the same authors describe the isolation of benzoylheteratisine, C29H3,03N, m.p. 213-4°, [a]jf° + 73° (EtOH), which yields a hydrochloride, m.p. 218-221° (dec.), and is hydrolysed to benzoic acid and heteratisine the latter they suggest may not exist naturally in the plant but may be produced from benzoylheteratisine during extraction. 

On acidification of the waste w, there is formation of sulfurous acid (from excess Na2S03) and nitrous acid (from the NaN02). The former re-... 

Especially in dicotyledonous plant species such as tomato, chickpea, and white lupin (82,111), with a high cation/anion uptake ratio, PEPC-mediated biosynthesis of carboxylates may also be linked to excessive net uptake of cations due to inhibition of uptake and assimilation of nitrate under P-deficient conditions (Fig. 5) (17,111,115). Excess uptake of cations is balanced by enhanced net re-lea,se of protons (82,111,116), provided by increased bio.synthesis of organic acids via PEPC as a constituent of the intracellular pH-stat mechanism (117). In these plants, P deficiency-mediated proton extrusion leads to rhizosphere acidification, which can contribute to the. solubilization of acid soluble Ca phosphates in calcareous soils (Fig. 5) (34,118,119). In some species (e.g., chickpea, white lupin, oil-seed rape, buckwheat), the enhanced net release of protons is associated with increased exudation of carboxylates, whereas in tomato, carboxylate exudation was negligible despite intense proton extrusion (82,120). 

In addition to the expected o-aldehyde (68), it is also possible to isolate the unhydrolysed dichloro compound (69). Attack by CC12 at the p-position in (67c) yields the intermediate (70) which, unlike the intermediate for o-attack, has no H atom that can be lost, as H , to allow the ring to re-aromatise (70) thus just acquires a proton, on final acidification, to yield (69). The dichloro compound (69) owes its resistance to hydrolysis partly to its insolubility in the aqueous base medium, but also to the sterically hindered, neopentyl-type environment (cf. p. 86) of the chlorine atoms. 

Metals are temporarily attenuated as evaporite minerals on the surface or in secondary oxides and hydroxides in the tailings. The evaporites will re-dissolve in wet weather conditions and the secondary minerals become unstable with acidification of the tailings releasing these metals into the environment. 

Preparative Photolysis. The preparative photolysis of an aqueous solution (pH=8.5) of AETSAPPE (2.5 M) was conducted in a 1-inch diameter quartz test tube in a Rayonet Reactor (Southern New England Radiation Co.) fitted with 254 nm lamps. Within two hours the solution gelled and the reaction was terminated. Upon acidification the solution cleared, and the product could be re-precipitated by addition of base. This indicates loss of the thiosulfate functionality. The product was dissolved in dilute HC1, precipitated with acetone, and filtered. This process was repeated three times, and the final precipitate was washed with water. The product (20 to 30 mg) was dried in vacuo for 24 hours and stored in a dessicator until use. Comparison of the13 C NMR spectrum of the product with the starting AETSAPPE 13C NMR spectrum clearly shows that the thiosulfate methylene peak shifted upfield, from 39 ppm to 35 ppm. The complete 13 C NMR and IR analysis of the product were consistent with the disulfide product. Further, elemental analysis of the product confirmed that the product was the desired disulfide product 2-amino (2-hydroxy 3-(phenyl ether) propyl) ethyl disulfide (AHPEPED) Expected C 58.39, H 7.08, N 6.20, S 14.18 actual C 58.26, H 7.22, N 6.06, S 14.28. 

Ammonia has a lifetime of only a few hours to a few days in the atmosphere. It and its reaction products are transported through the atmosphere and deposited on terrestrial snrfaces elsewhere. It is the main gaseous alkaline species in the atmosphere and neutralizes a large part of the acid produced in oxidation of sulfur and nitrogen oxides, probably up to a half though its dry-deposition is much faster than that of NO and SO2 (Dentener and Crutzen, 1994). Dry- and wet-deposition of ammonia contribute to soil acidification because 2 mol of H+ are produced in the nitrification of Imol of NH4+. Also a large part of the ammonia deposited on moist forest soils may be re-emitted as N2O (Section 8.2). 

Although NH3 is not one of the greenhouse gases, NHs-emissions cause negative environmental effects through soil acidification and uncontrolled nitrogen re-circulation. The latter is due to ammonia losses from organic and mineral fertilisers and re-import from the atmosphere to soil by precipitation. 

Excretion of drugs will be affected by the pH of the urine. If the urine is acidic, weak bases are ionized and there will be poor re-absorption. With basic urine, weak bases are non-ionized and there is more re-absorption. The pH of the urine can be artificially changed in the range 5-8.5 oral administration of sodium bicarbonate (NaHCOs) increases pH values, whereas ammonium chloride (NH4CI) lowers them. Thus, urinary acidification will accelerate the excretion of weak bases and retard the excretion of weak acids. Making the urine alkaline will facilitate the excretion of weak acids and retard that of weak bases. 

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