formaldehyde - Sciencemadness Dot Org

120
FORMALDEHYDE
precipitates. Colloidal gold is formed by the action of formaldehyde on
gold chloride solution in the presence of potassium carbonate 11 .
Silver chloride is rapidly and quantitatively reduced to silver when
treated with formaldehyde in the presence of strong alkalies, whereas with
silver bromide and iodide the reduction proceeds slowly and is quantitative
only when special precautions are taken 111 . Under neutral or mildly acid
conditions, formaldehyde is said to reduce iron from its salt solutions as a
crystalline precipitate 2 . Kelber 64 obtained colloidal nickel by heating a
solution of nickel formate and gelatin in glycerol with formaldehyde.
Copper sulfate is reported not to be reduced by formaldehyde alone even
on prolonged heating at 100°C. S4 (see also page 345).
Ammonia. Formaldehyde and ammonia react to form hexamethylenetetramine
in quantitative yield. This reaction which was first observed
by Butlerov 17 was later studied by Duden and Seharf 25 , Eschweiler, and
many other investigators. Its formation and structure are indicated in
the equation shown below:
6CH20 + 4NH3
HsC
N
CH2 ca2
N
/ \
CH2 CH2
\ /
C
N
6H*0
Since hexamethylenetetramine is a formaldehyde product of considerablecommercial
importance and behaves chemically as a special form of anhydrous
formaldehyde in many industrial applications, its formation,,
manufacture, and properties are treated specifically in Chapter IS and
will not be further discussed in this place.
Reaction products other than hexamethylenetetramine may apparently
be obtained from ammonia and formaldehyde in special instances. Fosse's
studies of the mechanism by which urea, hydrogen cyanide, and other
nitrogenous compounds are formed in plants indicates that ammonia and
formaldehyde may be the precursors of these products 34 ' 35 . On oxidation
in the presence of ammoniacal silver and mercury salts, formaldehyde
is partly converted to hydrogen cyanide, from which urea can be produced