ning (Newbee)
10-23-03 15:01
No 466401
      Formic acid from ethanol     

Suppose everyone's heard this before, but in an old book, there was seen a statement that chloral (trichloroacetaldehyde), when subjected to NaOH, would decompose into Sodium Formate and Chloroform.
Wonderfully, this reaction does not evolve water, so you get two anhydrous useful substances.

So what? Ning, you said ALCOHOL! Yes, yes I did.
Chloral (when stirred with water giving chloral hydrate, another useful thing to have around) is produced by chlorinating ethanol. In the book ning dreamed of seeing, it said:

CH3.CH2.OH + 4Cl2 --> CCl3.CH.OH + 5HCl

Strangely, the chlorine was removing hydrogens, not only chlorinating the alcohol, but also transforming it into acetaldehyde. Ning doesn't know if this was a misprint, hallucination, or cold reality. In any case, for those among us who object to the use of chlorine, ning supposes one of the dichlorohydantoins, trichloroisocyanuric acid, or possibly even bleach could be used instead of chlorine. If this was in fact the case, it could be even easier to make formic acid than using oxalic acid and glycerin. Certainly, if luck, yields, and good lab skills are with us, this may not require any distillation apparatus.

certainly a cool synth, anyway.

Anybee heard of this route before?
 
 
 
 
    SPISSHAK
(Hive Addict)
10-23-03 15:15
No 466404
      looks nice on paper     

but in the real world it is'nt as feasible.
try the thermal decomp. of oxalic at around 160 C you get CO2 and HCOOH higer temps and different things happen.
Like CO and H2O formation.
 
 
 
 
    moo
(Hive Bee)
10-23-03 15:52
No 466415
      It is called the haloform reaction.     

It is called the haloform reaction. It has been discussed quite a lot in connection with synthesizing chloroform and various carboxylic acids, formic acid included. UTFSE and check out ../rhodium /chloroform.html too.

fear fear hate hate
 
 
 
 
    ning
(Newbee)
10-23-03 15:55
No 466416
      but....     

)I'm telling you, as far as I heard, it worked. It made it into a chem book! Might try to find what temp it was at, but not too high, if I remember correctly. Did you ever hear of this reaction before, or just shooting before taking aim?
(not to insult, of coursesmile
 
 
 
 
    lugh
(Moderator)
10-23-03 19:22
No 466448
      Organic Chemistry
(Rated as: excellent)
    


looks nice on paper
but in the real world it is'nt as feasible.




Actually, this route was used as an industrial method for producing chloroform, so it is practical, at least on a large scale cool From Perkin's Organic Chemistry wink

Chloral, or trichloraldehyde cannot be prepared by the direct action of chlorine on aldehyde; it is manufactured on a large scale by saturating alcohol with chlorine, first at ordinary temperatures, and then at the boiling point, the operation taking some days. The crystalline product, which consists for the greater part of chloral alcoholate,  is distilled with concentrated sulphuric acid, and the oily distillate of crude chloral converted into chloral hydrate. After purifying the hydrate by recrystallisation from water, it is distilled with sulphuric acid, when pure chloral passes over. The aldehyde first produced by the oxidising action of the chlorine, combining with alcohol, and being finally converted into chloral alcoholate by substitution.
It is, however, very doubtful whether the action is quite so simple. A more probable explanation is that acetal is first produced by the combination of the aldehyde with the unchanged alcohol, and then converted into trichloracetal, by the further action of chlorine; this substance is finally decomposed by the hydrogen chloride produced during the reaction, giving chloral alcoholate and ethyl chloride, Chloral is an oily liquid of sp. gr. 1.512 at 20°, and boils at 97°. It has a penetrating and irritating smell, and in chemical properties closely resembles aldehyde, a fact which was only to be expected, since it is a simple substitution product of aldehyde, and contains the characteristic aldehyde group. It has reducing properties, combines directly with ammonia, sodium hydrogen sulphite, etc., and on oxidation it is converted into trichloracetic acid, just as aldehyde is converted into acetic acid, On the addition of small quantities of acids, it readily undergoes polymerisation, being transformed into a white amorphous modification called metachloral; the same change takes place when chloral is kept for a considerable time. One of the most interesting reactions of chloral is its behaviour with boiling potash, by which it is quickly decomposed, giving chloroform and potassium formate. Pure chloroform is often prepared in this way. When chloral is poured into water, it sinks as an oil at first, but in a few seconds the oil changes to a mass of colourless crystals of chloral hydrate, a considerable rise in temperature taking place. Chloral hydrate melts at 57°, is readily soluble in water, and is decomposed on distillation with sulphuric acid, chloral passing over. In some respects it is a very stable substance; it does not polymerise, and does not give the rosaniline reaction of aldehydes. These facts point to the conclusion that chloral hydrate does not contain the aldehyde group. Chloroform, or trichloromethane, is formed when methane, methyl chloride, or methylene dichloride, is treated with chlorine in sunlight, and when many simple organic substances containing oxygen, such as ethyl alcohol, acetone, etc, are heated with bleaching powder, which acts as an oxidising as well as a chlorinating agent.
Chloroform may be prepared by distilling alcohol or acetone with bleaching powder: Some strong bleaching powder (about 450 grams) is made into a cream with about 1 litres of water contained in a large flask, and alcohol, methylated spirit, or acetone (about 100 c.c.) is gradually added; the flask is then connected with a condenser, and slowly heated on a water-bath, when a mixture of chloroform, water, and alcohol or acetone distils. If the operation has been successful, the chloroform collects as a heavy oil at the bottom of the receiver; but if too much alcohol or acetone be present, the chloroform must be precipitated by adding water. It is then separated with the aid of a funnel, washed with water, shaken once or twice with a little concentrated sulphuric acid, which frees it from water, alcohol, etc., and redistilled from a water-bath.
The chloroform prepared in this way is not quite pure; the pure substance is best prepared by distilling chloral or chloral hydrate, with caustic soda, the product being separated in the manner just described, The changes which occur in the preparation of chloroform from alcohol are complex; it is probable that aldehyde is first formed by oxidation, and then converted into chloral, which is decomposed by the calcium hydroxide which is always produced during the reaction, yielding chloroform and calcium formate. When acetone is employed, trichloracetone is probably formed in the first place; this compound is then decomposed by the calcium hydroxide, giving chloroform and calcium acetate, chloroform is a heavy, pleasant-smelling liquid of sp. gr. 1.498 at 15°, and boils at 61°; when strongly heated, it burns with a green-edged flame, but it is not inflammable at ordinary temperatures. It is readily decomposed by warm alcoholic potash, yielding potassium formate and chloride, Formic Acid, occurs in nature in nettles, ants (fornica;), and other living organisms; the sting of ants and nettles owes part, at least, of its irritating effect to the presence of formic acid. When nettles or ants are macerated with water and the mixture distilled, weak aqueous formic acid collects in the receiver.
Formic acid can be obtained from its elements by simple methods, When carbon monoxide is passed over moistened potassium hydroxide heated at 100°, it is slowly absorbed, and potassium formate is produced, When moist carbon dioxide is passed over potassium, formate and carbonate of potassium are formed, the carbon dioxide being reduced by the nascent hydrogen evolved during the interaction of the potassium and water. The acid may be obtained from the potassium salt by distilling with dilute sulphuric acid.
Formic acid can also be obtained by oxidising methyl
alcohol or formaldehyde with platinum black (precipitated platinum), and by heating hydrocyanic acid with alkalies or mineral acids, Formic acid is prepared by heating oxalic acid with glycerol (glycerin); it can be obtained by heating oxalic acid alone, but a large proportion of the acid sublimes without decomposition. Glycerol (about 50 c.c.) is placed in a retort con­nected with a condenser, crystallised oxalic acid (about 30 grams) added, and the mixture heated to about 100-110°; rather below this temperature, evolution of carbon dioxide commences, and dilute formic acid distils, but after keeping for some time at 100-110°, action ceases. A further quantity of oxalic acid is then added, and the heating continued, when carbon dioxide is again evolved, and a more concentrated solution of formic acid collects in the receiver. If an alkali be used, ammonia is liberated, and a salt of formic acid obtained; whereas when a mineral acid is employed, free formic acid and an ammonium salt are produced, By adding more oxalic acid from time to time, a large quantity of formic acid can be obtained, the glycerol, like the sulphuric acid in the manufacture of ether, being able, theoretically, to con­vert an unlimited quantity of oxalic into formic acid. When crystallised oxalic acid, is heated with glycerol, it loses its water of crystallisation; the anhydrous acid is then decomposed into carbon dioxide and formic acid; part of the latter distils with the water, part combining with the hydroxide, glycerol, to form the salt, glycerol formate, or monoformin, On adding more crystallised oxalic acid, the monoformin is decom­posed by part of the water expelled from the oxalic acid crystals, yielding glycerol and formic acid, the regenerated glycerol and the anhydrous oxalic acid then interact as before, yielding monoformin, carbon dioxide, and water.
In order to prepare anhydrous formic acid, the aqueous distillate is gently warmed and excess of litharge added in small quantities at a time, the solution being gradually heated to boiling; as soon as the litharge ceases to be dissolved, the solution is filtered hot, and the filtrate evaporated to a small bulk, when colourless crystals of lead formate are obtained, this salt is carefully dried, and about the of it introduced in the form of coarse powder, between plugs of cotton wool, into the inner tube of an upright Liebig's condenser, which is connected above with an apparatus for generating hydrogen sulphide, and below with a suitable receiver closed with a calcium chloride drying tube; the lead formate is heated by passing steam through the outer tube of the condenser, and carefully dried hydrogen sulphide is led over it, when anhydrous formic acid collects in the receiver, the acid is now placed in a retort connected with a condenser, the remainder of the dried lead salt added, and, after warming gently for a short time, the acid is distilled, care being taken to prevent absorption of moisture; this rectifica­tion or distillation over lead formate is necessary in order to free the acid from hydrogen sulphide.
Formic acid is a colourless, mobile, hygroscopic liquid of sp. gr. 1.241 at 0°; it solidifies at low temperatures, melting again at 8°, and boiling at 101°. It has a pungent, irritating odour, recalling that of sulphur dioxide, and it blisters the skin like a nettle sting does; it is miscible with water and alcohol in all proportions. The anhydrous substance and its aqueous solution have an acid reaction, decompose carbonates, and dissolve certain metallic oxides; formic acid, in fact, behaves like a weak mineral acid. Like the aldehydes, it has reducing properties, and precipitates silver from warm solu­tions of ammoniacal silver nitrate, being itself oxidised to carbon dioxide, When mixed with concentrated sulphuric acid, it is rapidly. and when heated alone at 160° in closed vessels, it yields carbon dioxide and hydrogen. The Formates, or salts of formic acid, are prepared by neutralising the acid with alkalies, hydroxides, etc., or by double decomposition; they are all soluble in water, but some, such as the lead and silver salts, only moderately easily; they are all decomposed by warm concentrated sulphuric acid, with evolution of carbon monoxide, and by dilute mineral acids, yielding formic acid. The sodium salt and the potassium salt, are deliquescent; when heated at about 250°, they are converted into oxalates with evolution of hydrogen, a reaction which may. be made use of for the preparation of pure hydrogen.


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