Formic acid,

Formic acid [64-18-6] (methanoic acid) is the first member of the homologous series of alkyl carboxyHc acids. It occurs naturally ia the defensive secretions of a number of insects, particularly of ants. Although the acid nature of the vapors above ants nests had been known since at least 1488, the pure acid was not isolated until 1671, when the British chemist John Ray described the isolation of the pure acid by distillation of ants (1). This remained the main preparative method for more than a century until a convenient laboratory method was discovered by Gay-Lussac (2). The preparation of formates using carbon monoxide was described by Berthelot in 1856. 

Formic acid was a product of modest industrial importance until the 1960s when it became available as a by-product of the production of acetic acid by hquid-phase oxidation of hydrocarbons. Since then, first-intent processes have appeared, and world capacity has climbed to around 330,000 t/yr, making this a medium-volume commodity chemical. Formic acid has a variety of industrial uses, including silage preservation, textile finishing, and as a chemical intermediate. 

In the vapor phase formic acid forms a hydrogen-bonded dimer  

At room temperature and atmospheric pressure, 95% of the vapor consists of dimers (13). The properties of the vapor deviate considerably from ideal gas behavior because of the dimeri2ation. In the soHd state, formic acid forms infinite chains consisting of monomers linked by hydrogen bonds (14)  

The chain stmcture persists in Hquid formic acid, but in solution in hydrocarbons the dimeric form predominates (15). 

CHEMICAL NAME = methanoic acid CAS NUMBER = 64-18-6 MOLECULAR FORMULA = HCOOH MOLAR MASS = 46.0 g/mol COMPOSITION = C(26.1°/o) 0(69.5%) H(4.4%) 

The usual commercial product is marketed as a solution of 90% formic acid in water. Anhydrous formic acid must be handled carefully it is a strong dehydrating agent and can cause severe skin burns. Formic acid is soluble in water, alcohol, ether, and glycerol. It is industrially synthesized by heating carbon monoxide and sodium hydroxide under pressure to form 

Exposure to formic acid is potentially dangerous. It irritates the skin, eyes, and mucous membranes and may also be toxic to the kidneys. Chronic exposure may lead to kidney damage or dermatitis. Acute exposure produces a variety of symptoms including eye irritation, blisters in the mouth and nasal membranes, headache, nausea, and breathing difficulties. Extreme exposure results in unconsciousness and death. 

The decomposition of formic acid has been a popular reaction for studying catalytic behaviour of inorganic as well as organic catalysts. The rate of formation of the products may be followed easily by studying the change of pressure in a closed system. However, the reaction, instead of being simple, is quite complicated from the chemical point of view. 

If the catalyst to be studied has acidic sites, formic acid may decompose into carbon-monoxide and water according to a class A mechanism (dehydration). We may assume the mechanism of decomposition to be that of an acid catalyzed decarboxylation 63  

Many catalysts however, especially the metallic ones, cause dehydrogenation instead, and the products of reactions are hydrogen and carbon dioxide. 

In the many studies that have been done using metallic catalysts, it has been shown that the adsorbed species is a formate ion So the chemisorbtion step in the dehydrogenation reaction involves a heterolytic splitting of the OH-bond  

Therefore in cases where this step is rate determining, as could be shown for metals like gold 64 acid/base properties of the catalyst enter into the picture of the dehydrogenation reaction. 

A small excess of undissociated formic acid has a stronger bactericidal effect on the culturability of Campylobacter jejuni and Campylobacter coli in comparison with a large excess of undissociated propionic or acetic acid at the same pH levels. It may be possible that the structure of these acids is the most important factor in the inhibition activity of C. jejuni and C. coli viability (Chaveerach et al., 2002). 

0 L/min is passed over coconut shell charcoal. The analyte is desorbed with 1 mL of formic acid, allowed to stand for an hour, and injected into a GC equipped with an FID. Suitable GC columns for this analysis are 0.3% SP-1000 + 0.3% H3PO4 on Carbopack A, 0.3% Carbowax 20M -I- 0.1% 

H3PO4 on Carbopack C, and Carbopack B 60/80 mesh -I- 3% Carbowax 20M -I- 0.5% H3PO4. This method should also be effective for the analysis of C3- and C4- carboxylic acids in air. 

EPA Designated Toxic Waste, RCRA Waste Number U123 DOT Label Corrosive Material, UN 1779 

Formic acid occurs in the stings of ants and bees. It is used in the manufacture of esters and salts, dyeing and finishing of textiles and papers, electroplating, treatment of leather, and coagulating rubber latex, and also as a reducing agent. 

Formic acid is a low to moderately toxic but highly caustic compound. It is corrosive 

Distillation in Steam.—The apparatus for distilling in steam is shown in Fig. 68. A. laige flask, or, pieferably, a i gallon 

The powdered salt, dried on tlie wtvtt-r-bath, is introduced in a long layer into a sloping vvido tiihe, 

Colouiless liquid, with a penetrating smell rc -semblmg sulphurous acid, b. p. 100° sp.gr. 1-223 at o solid ilii--. below o to colourless crystals m. p. 8 6 soluble in water iiul alcohol. 

Renciio/is Foi the follow-ing tests use a neutral solution pared as follows —Boil a little lead formate with a soltitioii ol 

Add to the solution a few drops of a solution of silver nitrate and wai 111. Mcttdlic silver is deposited as a black poit der. 

At the natural pH of the solution, sodium formate is oxidised by silver nitrate. The following kinetics have been reported in an early study  

A re-investigation of this reaction under controlled conditions of acidity and ionic strength is desirable. 

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Figure 3-6. Fugacity coefficients for saturated mixtures containing two carboxylic acids formic acid (1) and acetic...

Two additional illustrations are given in Figures 6 and 7 which show fugacity coefficients for two binary systems along the vapor-liquid saturation curve at a total pressure of 1 atm. These results are based on the chemical theory of vapor-phase imperfection and on experimental vapor-liquid equilibrium data for the binary systems. In the system formic acid (1) - acetic acid (2), <() (for y = 1) is lower than acetic acid at 118.2°C. Since strong dimerization occurs between all three possible pairs, (fij and not... 

The largest errors in predicted compositions occur for the systems acetic acid-formic acid-water and acetone-acetonitrile-water where experimental uncertainties are significantly greater than those for other systems. 

Momany F A 1978 Determination of partial atomic charges from ab initio molecular electrostatic potentials. Application to formamide, methanol and formic acid J. Phys. Chem. 82 592... 

Carbon monoxide is formed by the incomplete combustion of carbon. It is prepared in the laboratory by dropping methanoic (formic) acid into warm concentrated sulphuric acid the latter dehydrates the methanoic acid ... 

Formic Acid, HCOOH (in aqueous solution), and Lead Formate, (HCOO)2Pb. 

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. 

A considerable amount of the formic acid, however, still remains behind in the distilling-flask as the unhydrolysed monoformate. Therefore, if time allows, dilute the residue in the flask with about an equal volume of water, and then steam-distil, the monoformate ester being thus completely hydrolysed and the formic acid then driven over in the steam. Collect about 400 ml. of distillate. Add this distillate to that obtained by direct heating of the reaction mixture and then treat with lead carbonate as described above. Total yield of lead formate is now about 40 g. 

Lead formate separates from aqueous solution without water of crystallisation. It can therefore be used for the preparation of anhydrous formic acid. For this purpose, the powdered lead formate is placed in the inner tube of an ordinary jacketed cond ser, and there held loosely in position by plugs of glass-wool. The condenser is then clamped in an oblique position and the lower end fitted into a receiver closed with a calcium chloride tube. A current of dry hydrogen sulphide is passed down the inner tube of the condenser, whilst steam is passed through the jacket. The formic acid which is liberated... 

If the reaction mixture used in the above preparation of formic acid is heated to 190-200°, the glyceryl monoformate which has escaped hydrolysis undergoes decomposition, with the loss of carbon dioxide and water, and the... 

In the following examples, pinacol is oxidised to acetone, which is identified as its semicarba2one and its 2,4 dinitrophenylhydra2one, and glycerol is oxidised to formaldehyde and formic acid. The formaldehy de is readily detected by the condensation product which it gives with dimedone, 5,5-dimethylcyclohexan-i,3-dione (p, 277). 

When a solution of nitrobenzene in methanol is boiled with sodium hydroxide, the nitrobenzene is reduced to azoxybenzene by the methanol, which is itself oxidised to formic acid. 

The Formaldehyde-Formic Acid Method, This method applies to primary and secondary amines, which when boiled with a formalin-formic acid mixture undergo complete methylation to the corresponding tertiary amine. This method has the advantage over the dimethyl sulphate method in that quaternary salts clearly cannot be formed. 

This reaction is given by most aromatic aldehydes having the aldehyde group directly joined to the benzene ring it is also given by formaldehyde, with the formation of methanol and formic acid. Other aliphatic aldehydes do not give Cannizzaro s reaction under these conditions. 

Oxidation, (i) Dissolve 5 g. of potassium dichromate in 20 ml. of dil. H2SO4 in a 100 ml. bolt-head flask. Cool and add 1 ml. of methanol. Fit the flask with a reflux water-condenser and warm gently a vigorous reaction soon occurs and the solution turns green. The characteristic pungent odour of formaldehyde is usually detected at this stage. Continue to heat for 3 minutes and then fit the flask with a knee-tube (Fig. 59, p. 100) and distil off a few ml. Test the distillate with blue litmus-paper to show that it is definitely acid. Then apply Test 3 p. 350) for formic acid. (The reflux-distillation apparatus (Fig. 38, p. 63) can conveniently be used for this test.)... 

Physical properties. All are colourless crystalline solids except formic acid, acetic acid (m.p. 18 when glacial) and lactic acid (m.p. 18°, usually a syrup). Formic acid (b.p. loo ") and acetic acid (b.p. 118 ) are the only members which are readily volatile lactic acid can be distilled only under reduced pressure. Formic and acetic acids have characteristic pungent odours cinnamic acid has a faint, pleasant and characteristic odour. 

Carbon monoxide test. Warm together carefully 0 5 ml. of formic acid (or 0 5 g. of a formate) and i ml. of cone. 112804. Identify the carbon monoxide by igniting the gas evolved and observing the pale blue flame travel down the test-tube. Note that dilute solutions of formic acid will not give this test. HCOOH — HjO — CO. 

Mercuric chloride test. Add mercuric chloride solution to formic acid or a solution of formate and w arm. A white precipitate of mercurous chloride, insoluble in dil. HCl, is produced. Sometimes the reduction proceeds as far as metallic mercury, which appears as a grey precipitate. 

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. 

Note. Oxalates do not reduce alkaline KMnO in the cold (cf. Test 3 (b) for formic acid), and only extremely slowly on heating.)... 

Oxidation, (a) Unsaturation test. Dissolve about o-i g. of cinnamic acid or of a soluble cinnamate in about 5 ml. of 10% NajCOg solution. To the cold solution add 1% aqueous KMn04 drop by drop. Immediate decolorisation denotes unsaturation. (Note. Many easily oxidisable substances, e.g.y formic acid, acetaldehyde, etc.y also rapidly decolorise alkaline permanganate. Cinnamates, however, do not reduce Fehling s solution.)... 

Chloroform and iodoform give also sodium formate in this reaction CHCI3 -h 4NaOH = HCOONa -h 3NaCl -f zH O. A portion of the solution, before the addition of the HNO3, should therefore be tested for formic acid (Tests, p. 350) ensure however that the solution is neutralised where necessary during these tests. 

Pungent odour. Formic acid, acetic acid, acetyl chloride, acetic anhydride, benzoyl chloride, benzyl chloride, pyridine. Benzoquinone (when warmed with water). 

Method, Formaldehyde may be estimated in solution by oxidising it to formic acid by means of a known quantity (in excess) of iodine dissolved in a excess of NaOH solution. The oxidation is, in effect, carried out by the odium hypo-iodite formed by the action of the iodine on the alkali, the formic cid being then neutralised by the alkali present ... 

Since formaldehyde solutions almost invariably contain formic acid, and amino-acids themselves are seldom exactly neutral, it is very important that both the formaldehyde solution and the glycine solution should before mixing be brought to the same pH (see footnote, p. 509), and for this purpose each solution is first madejWl alkaline to phenolphthalein by means of dilute sodium hydroxide solution. This preliminary neutralisation must not be confused with... 

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