ACIDIFICATION

3 Acid Mine Drainage and Ochreous Deposits. One of the major pollution problems alfecting freshwaters is that of acid waters dis- 

When mining and pumping cease, the water table returns to its natural level. While the flooding of the mine stops the direct oxidation of pyrite, it does bring the sulfuric acid and iron sulfates into solution. Some of the ferrous ion (Fe ) may be oxidized to the ferric ion (Fe ), a slow process at low pH, but one which can be catalysed by bacteria, and the ferric ion may react further with pyrite.  

Underground in the Richmond Mine at Iron Mountain, California, extremely acidic mine waters have been encountered, with pH ranging from 1.5 to —3.6 and total dissolved metal (mainly iron) and sulfate concentrations as high as 200 g and 760 g respectively. These are the most acidic waters known. 

Microorganisms e.g. Thiobacillus thiooxidans, Thiobacillus ferrooxi-dans, Metallogenium) are involved as catalysts in many of the oxidizing 

Some of the largest waste deposits occur in tailing ponds containing acid mine water. In the Clark Fork River Complex, it is estimated that 

Members of three genera are used as cheese starters. For cheeses that are cooked to a temperature below about 39°C, species of Lactococcus, usually Lc. lactis ssp. cremoris, are used, i.e. for Cheddar, Dutch, Blue, surface mould and surface-smear families. For high-cooked varieties, a thermophilic Lactobacillus culture is used, either alone (e.g. Parmesan) or with Streptococcus salivarius ssp. thermophilus (e.g. most Swiss varieties and Mozzarella). Leuconostoc spp. are included in the starter for some cheese varieties, e.g. Dutch types the function is to produce diacetyl and CO2 from citrate rather than acid production. 

The selection, propagation and use of starters will not be discussed here. The interested reader is referred to Cogan and Hill (1993). 

Acid production plays several major roles in cheese manufacture  

Organism Transport Cleavage enzyme Pathway s Products (mol mol lactose) 

The primary starter performs several functions in addition to acid production, especially reduction of the redox potential (f, from about + 250 mV in milk to —150 mV in cheese), and, most importantly, plays a major, probably essential, role in the biochemistry of cheese ripening. Many strains produce bacteriocins which control the growth of contaminating micro-organisms. 

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Obtained synthetically by one of the following processes fusion of sodium ben-zenesulphonate with NaOH to give sodium phenate hydrolysis of chlorobenzene by dilute NaOH at 400 C and 300atm. to give sodium phenate (Dow process) catalytic vapour-phase reaction of steam and chlorobenzene at 500°C (Raschig process) direct oxidation of cumene (isopropylbenzene) to the hydroperoxide, followed by acid cleavage lo propanone and phenol catalytic liquid-phase oxidation of toluene to benzoic acid and then phenol. Where the phenate is formed, phenol is liberated by acidification. 

Schweizer s reagent The dark blue solution obtained by dissolving Cu(OH)2 in concentrated ammonia solution. Used as a solvent for cellulose, the cellulose is precipitated on acidification. Used in the cuprammonium process for the manufacture of rayon. 

The liberated iodine is titrated with standard sodium thiosulphate(Vr) solution after acidification to remove the hydroxide ions. 

Anhydrous cupric sulphate is white but forms a blue hydrate and a blue aqueous solution. The solution turns yellow when treated with concentrated hydrochloric acid, dark blue with ammonia, and gives a white precipitate and brown solution when treated with potassium iodide. A yellow-brown aqueous solution of ferric chloride becomes paler on acidification with sulphuric or nitric... 

Refractionation of the low-boiling impurities gives a further quantity of the acetoacetate, but if the initial distillation has been carefully conducted, the amount recovered is less than i g., and the refractionation is not worth while. If possible, complete the preparation in one day. If this is not possible, it is best to allow the cold crude sodium derivative (before acidification) to stand overnight, the flask being closed by a cork carrying a calcium chloride tube the yield will now fall to about 38 g. Alternatively, the crude ester may be allowed to remain overnight in contact with the sodium sulphate, but in this case the yield will fall to about 30 g. 

The Reformatsky Reaction consists of the interaction of an ester of an a-halogeno-acid with an aldehyde, a ketone or another ester in the presence of zinc. For example, if a mixture of ethyl bromoacetate and benzaldehyde is heated with zinc, the latter undoubtedly first combines with the ethyl bromoacetate to form a Grignard-like reagent (reaction A), which then adds on to the benzaldehyde Just as a Grignard reagent would do (reaction B). The complex so formed, on acidification gives ethyl p-phenyl-p-hydroxy-propionate (reaction C). Note that reaction A could not satisfactorily be carried out using... 

Note also that if another ester, of general formula R-COOCjHj, were used in place of benzaldehyde in the above reaction, a similar complex would be formed, and on acidification would give an unstable p-hydroxy-P-ethoxy ester, which would very readily lose ethanol with the formation of a 3-keto-ester. 

As(ONa), -I- CH,I — [CH,As(ONa)jI] CH,AsO(ONa), — CH,AsO(OH), unstable product losing sodium iodide to form disodium methylarsonate, which on acidification liberates methylarsonic acid. Note that this synthesis is limited to alkylarsonic acids, whereas the Bart synthesis (p. 312) is limited to aiy larsonic acids. 

Nitrogen. To one portion of the filtrate, add z-3 ml. of 10, aqueous sodium hydroxide solution, then add about o-2 g. of ferrous sulphate and proceed as in the Lassaigiie nitrogen test (p, 322). Note, however, that the fiUal acidification with dilute siiphiiric acid must be made with care, owing to the vigorous evolution of carbon dioxide from the carbonate present. 

Action of sodium hydroxide. Does not undergo the Cannizzaro reaction. It dissolves in dil. NaOH solution, giving a yellow solution from which the aldehyde is precipitated unchanged on acidification. If heated with cone. NaOH solution, salicylaldehyde slowly undergoes atmospheric oxidation to salicylic acid. 

Amides (except urea and thiourea), imides and nitriles, after the above alkaline hydrolysis, give derivatives similarly to those from the alkaline solution obtained from ammonium salts (p. 360). (A) If the original compound is aromatic, acidification of the cold solution deposits the crystalline acid. (B) The cold solution, when carefully neutralised (p. 332) and treated with benzylthiuronium chloride, deposits the thiuromum salt. 

B) Benzoyl derivatives. Most amino-acids can be benzoyl-ated when their solutions in 10% aqueous sodium hydroxide are shaken with a small excess of benzoyl chloride until a clear solution is obtained (Schotten-Baumann reaction, p. 243). Acidification of the solution then precipitates the benzoyl derivative and the excess of benzoic acid, and the mixture must be filtered off, washed with water, and recrystallised (usually from ethanol) to obtain the pure derivative. (M.ps., p. 555 )... 

Principle. An organic compound which contains chlorine is mixed with sodium peroxide and ignited in a closed metal bomb. The chlorine is thus converted to sodium chloride, and after acidification the chloride is estimated by the Volhard volumetric method. Bromine and iodine, when constituents of organic compounds similarly treated, are converted largely into sodium bromate and iodate respectively these ions are therefore subsequently reduced by hydrazine to bromide and iodide ions, and estimated as before. 

By the ketonic hydrolysis of substituted acetoacetic esters this is brought about by the action of dilute alkali in the cold, followed by acidification and boiling. The free substituted acetoacetic acid is produced, which readily undergoes decarboxylation (since it has a carboxyl and a carbonyl group on the same carbon atom) to give a ketone, for example ... 

Dichloroacetic acid is conveniently prepared by the action of calcium carbonate in the presence of a little sodium cyanide upon chloral hydrate, followed by acidification with concentrated hydrochloric acid ... 

The free acids are obtained upon acidification. Fata usually consist of mixtures of glycerides. The term wax is usually applied to esters of fatty acids with other alcohols such as cetyl alcohol CH3(CH2),4CHjOH and oleyl alcohol CH3(CHj),CH=CH(CHj),CH30H. 

The equilibrium of the last step (3), which is not actually part of the condensation mechanism, is far to the right because of the greater basic strength of the ethoxide ion as compared to (IV), and this largely assists the forward reactions in (1) and (2). The reaction mixture contains the sodium derivative of the keto-ester, and the free ester is obtained upon acidification. 

Upon fusion with caustic alkah (for experimental details, see Section IV,33,2) and acidification of the aqueous extract, hydrogen sulphide is evolved (detected by lead acetate paper). This test is given by aU organic compounds of divalent sulphur (RSH, R SR" and R SSR"). 

Primary nitro compound intense red colour, disappearing upon acidification. The colouration is that of the alkali salt of the nitrolic acid (nitro oxime) -... 

Once the presence of a sulphonate group has been estabhshed (and, if possible, the phenol isolated), the compound may be characterised by the preparation of a derivative. It must be remembered that both sulphoxides RSOR and sulpJiones RSOjR yield sulphur dioxide on fusion with caustic alkali and acidification. 

Similarly aniline CgHjNHj is converted into benzonltrlle C3H5CN. Hydrolysis of the nitrile with so um hydroxide solution, followed by acidification, 3uelds the corresponding acid, for example ... 

Phenylhydrazine may be prepared by reducing phenyldiazonium chloride solution with excess of warm sodium sulphite solution, followed by acidification with hydrochloric acid, when the hydrochloride crystallises out on cooling. Treatment of the latter with excess of sodium hydroxide solution liberates the free base. The reaction is believed to proceed through the following stages —... 

Dissolve 0 01 mol (or 1 g. if the molecular weight is unknown) of the compound in 5 ml. of 3A sodium hydroxide solution, add 10-20 g. of crushed ice followed by 1-5 g. (1-5 ml.) of acetic anh3 dride. Shake the mixture vigorously for 30-60 seconds. The acetate separates in a practically pure condition either at once or after acidification by the addition of a mineral acid. Collect the acetyl derivative, and recrystallise it from hot water or from dilute alcohol. 

In the strongly basic medium, the reactant is the phenoxide ion high nucleophilic activity at the ortho and para positions is provided through the electromeric shifts indicated. The above scheme indicates theorpara substitution is similar. The intermediate o-hydroxybenzal chloride anion (I) may react either with a hydroxide ion or with water to give the anion of salicyl-aldehyde (II), or with phenoxide ion or with phenol to give the anion of the diphenylacetal of salicylaldehyde (III). Both these anions are stable in basic solution. Upon acidification (III) is hydrolysed to salicylaldehyde and phenol this probably accounts for the recovery of much unreacted phenol from the reaction. 

Upon acidification of the sodium carbonate washings, 4-5 g. of p-nitro benzoic acid, m.p. 242-243°, are recovered. 

Aromatic aldehydes react with the dimedone reagent (Section 111,70,2). All aromatic aldehydes (i) reduce ammoniacal silver nitrate solution and (ii) restore the colour of SchifiF s reagent many react with sodium bisulphite solution. They do not, in general, reduce Fehling s solution or Benedict s solution. Unlike aliphatic aldehydes, they usually undergo the Cannizzaro reaction (see Section IV,123) under the influence of sodium hydroxide solution. For full experimental details of the above tests, see under Ali-phalic Aldehydes, Section 111,70. They are easily oxidised by dilute alkaline permanganate solution at the ordinary temperature after removal of the manganese dioxide by sulphur dioxide or by sodium bisulphite, the acid can be obtained by acidification of the solution. 

The experimental details already given for the detection and characterisation of aliphatic esters (determination of saponification equivalents h3 diolysis Section 111,106) apply equally to aromatic esters. A sfight modification in the procediu-e for isolating the products of hydrolysis is necessary for i)henolic (or phenyl) esters since the alkaline solution will contain hoth the alkali phenate and the alkali salt of the organic acid upon acidification, both the phenol and the acid will be hberated. Two methods may be used for separating the phenol and the acid ... 

The acid is hberated upon acidification. Hydrolysis may also be efifected (but less readily and usuaUy not quite so satisfactorily) by boiling with dilute h3 drochloric acid (1 1) or 20 per cent, sulphuric acid ... 

The methyl benzoate is removed by extraction with chloroform, and upon cautious acidification of the aqueous layer perbenzoic acid is liberated the latter is extracted with chloroform and is usually preserved as a solution in this solvent ... 

Trimethylene dibromide (1 mol) condenses with ethyl malonate (1 mol) in the presence of sodium ethoxide (2 mols) to form ethyl cydobutane-1 1-dksrboxylate (I). Upon hydrolysis of the latter with alcoholic potassium hydroxide, followed by acidification cyciobutane-1 1-dicarboxylic acid (II) is obtained. 

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