Solutions, formaldehyde Density

After adding p-rosaniline and formaldehyde, the colored solution was diluted to 25 ml in a volumetric flask. The absorbance was measured at 569 nm in a 1-cm cell, yielding a value of 0.485. A standard sample was prepared by substituting a 1.00-mL sample of a standard solution containing the equivalent of 15.00 ppm SO2 for the air sample. The absorbance of the standard was found to be 0.181. Report the concentration of SO2 in the air in parts per million. The density of air maybe taken as 1.18 g/L. 

Urea.—Forma.IdehydeResins. Cellular urea—formaldehyde resins can be prepared in the following manner an aqueous solution containing surfactant and catalyst is made into a low density, fine-celled foam by dispersing air into it mechanically. A second aqueous solution consisting of partially cured urea—formaldehyde resin is then mixed into the foam by mechanical agitation. The catalyst in the initial foam causes the dispersed resin to cure in the cellular state. The resultant hardened foam is dried at elevated temperatures. Densities as low as 8 kg/m can be obtained by this method (117). 

Technical formalin contains 8-10 per cent of methyl alcohol, so that it is not possible to use the table of densities (Note i of the preparation) for determining the formaldehyde content of the solutions. For example, a solution containing 37 per cent of formaldehyde and 10 per cent of methyl alcohol would have a density of 1.09 and correspond to 28 per cent of formaldehyde in pure water. In view of this, the recorded yield should probably be 64-66 per cent instead of 86-89 cent. 

Fuel cells using directly liquid fuels are advantageous in this aspect. Methanol, formaldehyde (water solution), formic acid (water solution) and hydrazine are among fuels relatively easy to oxidize electrochemically. Alcohol and hydrocarbon with larger molecular weight are much harder to oxidize completely to C02- Other qualifications to be considered are price, availability, safety, energy density and ease of handling. 

The mechanism for replacement of a methoxyl group by cyanide in these reactions follows Scheme 6.7. The radical-cation reacts with cyanide ion at the point of highest positive charge density. Oxidation of the radical so formed to the carbon-ium ion is followed by elimination of proton and formaldehyde [79]. The elimination step is analogous to the conversion of cyanhydrins to the carbonyl compound and cyanide ion in basic solution. 

Oxidation of Methane. A variety of new catalyst systems have been disclosed, and new reagents were developed with the aim to perform selective transformation of methane to methanol, methyl esters, and formaldehyde. Much work was carried out in strongly acidic solutions, which enhances the electrofilicity of the metal ion catalyst, and the ester formed is prevented from further oxidation. An important advance in the selective oxidation of methane to methanol is Periana s 70% one-pass yield with high selectivity in sulfuric acid solution under moderate conditions.1073 The most effective catalyst is a Pt-bipyrimidine complex. Pt(II) was shown to be the most active oxidation state generating a Pt-methyl intermediate that is oxidized to yield the product methyl ester. A density functional study... 

In the acid-catalyzed formaldehyde condensation, position 6 appeared to be the most reactive since in acid solution the relative electron density is... 

While these experiments, which were carried out without giving a theoretical insight into the nature of the electrochemical reaction, yielded almost all the possible oxidation products in the oxidation of methyl alcohol, Elbs and Brunner 2 have discovered a method which gives 80% of the current yield in formaldehyde. This is exactly the substance which could not be proven present up to that time among the electrolytic oxidation products of methyl alcohol. Elbs and Brunner electrolyzed an aqueous solution of 160 g. methyl alcohol and 49 to 98 g. sulphuric acid in a litre. They employed a bright platinum anode in an earthenware cylinder, using a current density of 3.75 amp.1 and a temperature of 30°. Only traces of formic acid and carbonic acid and a little carbon monoxide, aside from the 80 per cent, of formaldehyde, were formed. Plating the platinum anode with platinum decreased the yield of formaldehyde at the expense of the carbon dioxide. With an anode of lead peroxide the carbon dioxide exceeded the aldehyde. 

Fig. 12. Depemlence of viscosity, loss angle tangent and optical density on time of curing of a melamine-formaldehyde resin in solution and in bulk [81]. T = 80°. Concentration of fte solution 40% (1) 50% (2) 57% (3)...

The following table showing the relation between the density of formalin solutions and their formaldehyde content has been found useful. It is copied from Beilstein s Handbuch... 

Figure 3.18 Change in electrical resistance of an anion exchange membrane (strongly basic anion exchange) with and without anionic polyelectrolyte layers in the presence of sodium tetradecyl sulfate (STS). 1. without the layers and with STS 2. with the layers (immersion time 4 h) and with STS 3. with the layers (immersion time 24 h) and with STS 4. with the layers and without STS 1 left vertical axis 2,3 and 4 right vertical axis. After an anion exchange membrane had been immersed in 100ppm anionic polyelectrolyte (polycondensation product of sodium naphthalene sulfonate and formaldehyde MW ca. 1000) solution for the respective time at room temperature, electrodialysis was carried out at a current density of 2.5 mAcmr2 using 0.10 N sodium chloride solution containing 2.16 X 10 3 mol dm3 of STS.

Detection and Determination of Aldehyde. The amount of formaldehyde in methanolic reaction mixture was estimated quantitatively according to the procedure by Kolthoff (16). A series of solutions containing varying amounts (5 X 10" to 5 X lO M) of formaldehyde as well as the unknown sample, with pH adjusted to 3 by phosphate-citric acid buffer, was treated with 1.5 X lO M Schiff s reagent (3i). Thirty minutes later, the optical density at 5500 A. was determined by a Coleman Junior spectrometer. The unknown concentration of formaldehyde was estimated by interpolating the known values. This procedure was reproducible for autoxidation of ferrous chloride in methanol. However, in the presence of a reactive cosubstrate, such as benzoin, the color became unstable, and the analysis was only semiquantitative. It was possible to determine acetaldehyde quantitatively in ethanolic reaction mixtures by vapor chromatography using a decylphthalate column at 66°-68°C. 

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