Oxalic: acid

Oxalic acid occurs in the leaf blades of rhubarb. Pure oxalic acid is a white crystalline solid. 

These are compounds with two carboxyl (-COOH) groups in their structure. Their general formula is HOOC - (CH2)n - COOH. All dicarboxylic acids have common names. 

Some dicarboxylic acids are important monomers used in synthesizing polymers. For example, adipic acid (COOH(CH2)4COOH) is used for synthesizing nylon. 

In dicarboxylic acids, ionization of the second carboxyl group occurs less readily than the ionization of the first. Thus, K values of dicarboxylic acids are bigger than their K values. 

This occurs as a free acid in beet leaves, sorrel, spinach, asparagus, tobacco, and tomatoes. Its name comes from Latin oxolis which means sorrel one of the acid s primary sources. 

I Oxalic acid is one of the first organic acids to have been 

Oxalic acid occurs naturally in a number of vegetable products, including spinach, rhubarb, tea, chocolate, oats, 

Oxalic acid. Red atoms are oxygen white atoms are hydrogen and black atoms are carbon. Gray sticks indicate double bonds, publishers 

Traditionally, oxalic acid has been extracted from natural products by treating them with an alkaline solution, followed by crystallization of the acid. Sodium hydroxide is the alkaline material most commonly used for this procedure. Today, a number of methods are available for the commercial preparation of oxalic acid. In one procedure, carbon monoxide gas is bubbled through a concentrated solution of sodium hydroxide to produce oxalic acid. Alternatively, sodium formate (COONa) is heated in the presence of sodium hydroxide or sodium carbonate to obtain the acid. Another popular method of preparing oxalic acid involves the oxidation of sucrose (common table sugar) or more complex carbohydrates using nitric acid as a catalyst. The reaction results in the formation of oxalic acid and water as the primary products. 

Over a half million kilograms (about 1 million pounds) of oxalic acid are produced in the United States each year. 

Methacrylic acid polymerizes readily. The reaction is exothermic. The rate of reaction accelerates on heating, which may resnlt in violent rupture of closed containers. The polymerization may be inhibited with a trace quantity of hydroquinone and hydroquinone monomethyl ether (Aldrich 2006). The acid may be stored safely below its melting point. 

Addition of oxalic acid to chromic acid for the anodizing of A1 alloy has been reported to modify the morphology and improve the corrosion performance of anodic films (Moutar-lier et al. 2004). Also, it is a very effective additive for the ozone treatment of cellulose. It prevents the degradation of cellulose from ozone bleaching. 

White powder (anhydrous) or colorless crystals (dihydrate) odorless hygroscopic the anhydrous acid melts at 189.5°C (373.1°F) (decomposes) and the dihydrate melts at 102 C (215.6 F) sublimes at 157°C 

Oxalic acid may be absorbed into the body through skin contact. It is corrosive to the skin and eyes, producing bums. Dilute solutions of 10% strength may be a mild irritant to human skin. However, the inhalation toxicity is low because of its low vapor pressure. Airborne dusts can produce eyebum and irritation of the respiratory tract. 

TLV-TWA for anhydrous acid 1 mg/m (ACGIH, MSHA, and OSHA) TLV-STEL 2 mg/m (ACGIH). 

As oxalic acid is the product obtained by this hydrolysis it must have the constitution as represented, i.e., it is di-carboxyl. In fact, when cyanogen is hydrolyzed ammonium oxalate is obtained which, of course, results from the combination of the oxalic acid and ammonia as first formed. 

From Glycol.—A second synthesis which proves the constitution of oxalic acid is that from ethylene glycol, HO—CH2—CH2—OH. On the complete oxidation of glycol with nitric acid oxalic acid is obtained. This is plainly the oxidation of each of the primary alcohol groups to carboxyl, and may be represented as follows, 

From Hexa-chlor Ethane.—It may also be prepared by oxidizing a derivative of ethane, viz., hexa-chlor ethane, CCle, with potassium hydroxide. This reaction may be considered as yielding the complete oxidation product of ethane by the replacement of the six chlorine atoms by six hydroxyl groups. This then loses water, as in the case of all compounds which contain more than one hydroxyl group linked to one carbon atom, and di-carboxyl, or oxalic acid results, as follows. 

Oxidation Products of Ethane —Oxalic acid is thus the simplest di-carboxy acid possible. It may be considered as derived from ethane by the oxidation of both methyl groups to primary alcohol, aldehyde, and carboxyl groups successively. The entire series of oxidation relationships, including all of the intermediate compounds which we have already discussed, may be represented as follows  

1 CH3 Acetic aldehyde 1 1 CH2OH Glycolic aldehyde 1 1 CHO Glyoxal 1  

This is an typical example of a dicarboxylic acid in that C-C cleavage is the only route for oxidation. No study of the Co(III) oxidation has been made although it is highly probable that reaction would proceed through an oxalate complex. The thermal decomposition of Co(Ox)3 has been shown to be a first-order process and probably involves an internal redox reaction, viz. 

The lack of exchange between C-labelled oxalate in solution and bound oxalate rules out the existence of free C2O4 in this reaction. The same intermediate is thought to participate in isotopic Co(II)-Co(llI) exchange in oxalate solution . 

The most recent study indicates that both 0(0204)2(1120) and 0(0204)3 decompose by the dissociation of one end of the chelate to give an intermediate (1) capable of attacking a second molecule of complex to give 0 and 02 without participation of free radical intermediates, viz. 

The kinetics of the Ce(IV) sulphate oxidation of oxalic acid are simple second order although the rate coefficient is inversely proportional to both hydrogen and bisulphate-ion concentrations, and it is also reduced at very high oxalic acid concentrations. Values of the activation energy from 13.4+1.5 (ref. 411) to 16.5+0.4 (ref. 409) kcal.mole have been reported. An intermediate has been detected spectroscopically this decays in first-order fashion with E = 10.5+0.5 kcal.mole and with a rate independent of acidity. However, the extent of formation of this complex is reduced as the acidity is increased , and it appears that a less reactive dioxalato complex is formed at higher substrate concentrations . 

The oxidation by Mn(lII) chloride involves three complexes and the kinetic data of Taube are summarised in Table 15. The greater thermal stability of the /m-complex is considered to result from the lowering of the free energy relative to the transition state as compared with bis- and mono-complexes. The study of MnC204 was based on the Mn(III)-catalysed chlorine oxidation of oxalic acid.  

See FEollow-fibermembranes Membrane technology Reverse osmosis. 

Oxahc acid was synthesi2ed for the first time ia 1776 by Scheele through the oxidation of sugar with nitric acid. Then, Wn h1er synthesi2ed it by the hydrolysis of cyanogen [460-19-5] ia 1824. 

The potassium or calcium salt form of oxaUc acid is distributed widely ia the plant kingdom. Its name is derived from the Greek o ys, meaning sharp or acidic, referring to the acidity common ia the foflage of certain plants (notably Oxalis and Mmex) from which it was first isolated. Other plants ia which oxahc acid is found are spinach, rhubarb, etc. Oxahc acid is a product of metabohsm of fungi or bacteria and also occurs ia human and animal urine the calcium salt is a principal constituent of kidney stones. 

Oxahc acid is used in various industrial areas, such as textile manufacture and processing, metal surface treatments (qv), leather tanning, cobalt production, and separation and recovery of rare-earth elements. Substantial quantities of oxahc acid are also consumed in the production of agrochemicals, pharmaceuticals, and other chemical derivatives. 

The physical and thermochemical constants of anhydrous oxahc acid and oxahc acid dihydrate are summari2ed in Table 1. 

Chemical synthesis bleaches metal polish rust remover 

Colorless crystals. Dihydrate mp, 101-102°C anhydrous mp, 189.5T (dec) sublimes at 157T.1 

Soluble in water, alcohol, and glycerol slightly soluble in ether insoluble in benzene, 

Sodium Chlorite and Water. Addition of water to a mixture of sodium chlorite and oxalic acid results in the formation of highly explosive chlorine dioxide.3 

Caustic and corrosive to skin and mucous membranes.1 Dust irritates the respiratory system and eyes. Splashing solution into the eyes also causes irritation.4 Swallowing can cause severe internal pain, renal damage, convulsions, coma, and death from cardiovascular collapse.1 Avoid contact with eyes and skin.4 TLV-TWA 1 mg/m3 TLV- 

Wear nitrile rubber gloves, laboratory coat, eye protection, and a face shield. Cover the spill with a 1 1 1 mixture by weight of sodium carbonate or calcium carbonate, clay cat litter (bentonite), and sand. Scoop the mixture into a plastic pail and, in the fume hood, very slowly add the mixture to a pail of cold water. Allow to stand 24 hours. Test the pH of the solution and neutralize if necessary with sodium carbonate. Wash the solution into the drain. Treat the solid residue as normal refuse.4 6 

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Tertiary butyl alcohol, trimethyl carbinol, tertiary butanol. 2-methyl-2-propanol, Me3COH. Colourless prisms, m.p. 25°C, b.p. 83°C. Prepared by absorbing isobutene (2-methylpropene) in sulphuric acid, neutralizing and steam distilling the liquor. Converted to isobutene by heating with oxalic acid. Potassium-/-buloxide is a very strong base. 

Melbylpropene, isobutylene, isobutene, Me2C CH2 Prepared by heating r-butanol with oxalic acid. 

Crystallizes from water in large colourless prisms containing 2H2O. It is poisonous, causing paralysis of the nervous system m.p. 101 C (hydrate), 189°C (anhydrous), sublimes 157°C. It occurs as the free acid in beet leaves, and as potassium hydrogen oxalate in wood sorrel and rhubarb. Commercially, oxalic acid is made from sodium methanoate. This is obtained from anhydrous NaOH with CO at 150-200°C and 7-10 atm. At lower pressure sodium oxalate formed from the sodium salt the acid is readily liberated by sulphuric acid. Oxalic acid is also obtained as a by-product in the manufacture of citric acid and by the oxidation of carbohydrates with nitric acid in presence of V2O5. 

CHjCOCOOH. A colourless liquid with an odour resembling that of ethanoic acid, m.p. 13 C, b.p. 65 C/lOmm. It is an intermediate in the breakdown of sugars to alcohol by yeast. Prepared by distilling tartaric acid with potassium hydrogen sulphate. Tends 10 polymerize to a solid (m.p. 92 C). Oxidized to oxalic acid or ethanoic acid. Reduced to ( + )-Iactic acid. 

The reaction usually proceeds with explosive violence and a better method of preparation is to heat, gently, moist crystals of ethane-dioic acid (oxalic acid) and potassium chlorate(V) ... 

Naphthalene, oxalic acid (hydrated), cinnamic acid, acetamide, benzamide, m-dinitrobenzene,/>-nitrophenol, toluene p-sulphon-... 

Certain aliphatic compounds are oxidised by concentrated nitric acid, the carbon atoms being split off in pairs, with the formation of oxalic acid. This disruptive oxidation is shown by many carbohydrates, e.g., cane sugar, where the chains of secondary alcohol groups, -CH(OH)-CH(OH)-CH(OH)CH(OH)-, present in the molecule break down particularly readily to give oxalic acid. 

When a mixture of anhydrous glycerol and crystalline oxalic acid, (C00H)2,2H lO, is heated the glycerol undergoes esterification, givang first glyceryl monoxalate (A) the latter, however, decomposes as the temperature... 

CH2(0H)CH(0H)CH2(0H) + HCOOH reaches about 100°, losing carbon dioxide and giving glyceryl monoformate (B). On further heating, particularly if more oxalic acid is added, the mono formate is hydrolysed (the necessary water being provided both by the oxalic acid and by the first reaction), and consequently a distillate of aqueous formic acid is obtained. 

Required Glycerol, 70 ml. oxalic acid, 40 g. lead carbonate. 

The oxalate is prepared in a similar way, using a solution of 1 2 g. of oxalic acid in about 15 ml. of water. On stirring the mixed solutions with a rod, the oxalate crystallises out. 

Note. Methyl oxalate, unlike most other esters, hydrolyses very rapidly in aqueous solution hence it will evolve CO in the above test, owing to the formation of methanol and free oxalic acid. 

Glycol gives the non-volatile oxalic acid. After heating the mixture under reflux for 10 minutes, transfer 2 ml. of the cold product to a test-tube and add 4 ml. of cone. H2SO4. Note the production of carbon monoxide and carbon dioxide on heating (p. 350). 

Sulphuric add test. To 0-5 g. of oxalic acid or of an oxalate, add I ml. of cone. H2SO4 and warm CO and COg are evolved (cf. formic acid). The CO burns with a blue flame. Detect the COg by passing the mixed gases evolved into lime-water. It is essential to test for the COj in a separate reaction, or (if the same test-tube is used) before testing for CO. 

Reduction of acid permanganate. Add a few ml. of dil. HgSO to 1 ml. of a solution of oxalic acid or of an oxalate. Warm gently and add a dilute solution of KMn04 drop by drop and note the decolorisation. 

Hydrolysis of methyl oxalate. The exceptionally rapid hydrolysis of rnethyl oxalate can be followed thus Dissolve 0 2 g. of finely powdered methyl oxalate in 10 ml. of water, and add i drop of phenolphthalein. Then add very dil. NaOH solution (1%) drop by drop until the solution just turns pink it will be noticed that the colour rapidly fades, but is restored on the Further addition of 1-2 drops of NaOH solution. The colour fades again and the addition can be repeated until hydrolysis is complete. Oxalic acid (with which methyl oxalate may be confused) gives a precise end-point when treated with NaOH solution in this way. 

NOTE. Many esters reduce Fehling s solution on warming. This reduction occurs rapidly with the alkyl esters of many aliphatic acids, but scarcely at all with similar esters of aromatic acids (f.g., ethyl oxalate reduces, but ethyl benzoate does not). Note also that this is a property of the ester itself thus both methyl and ethyl oxalate reduce Fehling s solution very rapidly, whereas neither oxalic acid, nor sodium oxalate, nor a mixture of the alcohol and oxalic acid (or sodium oxalate), reduces the solution. 

It follows that liquids of high boiling point should not be distilled from drying agent systems which have appreciable vapour pressures. An extreme case of this action is the dehydration of oxalic acid dihydrate by distillation over toluene or over carbon tetrachloride. 

Pinacol upon dehydration with acid catalysts e.g., by distillation from 6A sulphuric acid or upon refluxing for 3—4 hours with 50 per cent, phosphoric acid or hydrated oxalic acid) is transformed into methyl ter<.-butyr ketone or plnacolone ... 

Diethyl oxalate. Reflux a mixture of 45 g. of anhydrous oxalic acid (1), 81 g. (102-5 ml.) of absolute ethyl alcohol, 190 ml. of sodium-dried benzene and 30 g. (16-5 ml.) of concentrated sulphuric acid for 24 hours. Work up as for Diethyl Adipate and extract the aqueous laj er with ether distil under atmospheric pressure. The yield of ethyl oxalate, b.p. 182-183°, is 57 g. 

Anhydrous oxalic acid may be prepared by heating the finely-powdered A.R. crystallised acid, spread upon large clock glasses, in an electric oven at 105° for 6 hours, allowing to cool in a desiccator and storing in a tightly stoppered bottle. 

Urea oxalate is also sparingly soluble in amyl alcohol and since urea is soluble in this alcohol, the property may be utilised in separating urea from mixtures. An aqueous extract of the mixture is rendered slightly alkaline with sodium hydroxide solution and extracted with ether this removes all the basic components, but not urea. The residual aqueous solution is extracted with amyl alcohol (to remove the urea) upon adding this extract to a solution of oxalic acid in amyl alcohol crystalline urea oxalate is precipitated. 

The b.p. under diminished pressure has been given as 80-81°/18 mm. To obtain a very pure sample of the amine, dissolve 1 part (by weight) of the above product with a sohitiuii of 1-04 parts of crystallised oxalic acid in 8 parts of hot water, add a little deculeiirisiiig carbon, and tilter. The liltered solution deposits crystals uf the acid oxalate about o g. of tliis salt remains in each 100 ml. of... 

Supplement II, 2nd 1929 152-194 Oxalic acid, 502. Succinic acid, 601. Fumaric acid, 737... 

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