Formaldehyde, from decomposition

C-O, N-O, and N-C bonds, and this induces additional strain in the oxazine system 7 <2000EJ02613>. Extrusion of formaldehyde from iV-acetyl-2,1-benzoxazine 8 to give imine 9 involves a concerted breaking of both the C-C and N-O bonds <1996J(P2)1367>. The experimental barriers are lower than the theoretical one predicted by AMI for the decomposition of 8 in the gas phase. 

The presence of difluoroaminomethanol among the products can be accounted for by a reaction of difluoroamine formed in the abstraction reaction with formaldehyde. The latter could result from decomposition of the -CH2OCH3 radical to CH20 and -CH3 (122). 

The extent of lattice oxygen incorporation into the decomposition products is linked to the surface redox properties of the oxide. Recent SSIMS and FT-RAIRS studies have provided initial evidence for the transient formation of oxygen vacancies on the surface of TiO2(110). Henderson has proposed that surface oxygen vacancies may explain the formation of trace amounts of formaldehyde from formic acid on Ti02(l 10) (figure 3) [41]. Both reactions (6) and (7) are proposed to occur below 500 K the water produced from formic acid exposure desorbed at 475 K, before the onset of formate decomposition to form CO. Formaldehyde and CO2 were produced in minor quantities relative to the production of CO [41]. Formaldehyde was formed from formic acid on reduced... 

Fig. 48. Effect of the presence of sulphur on the Ni(lOll) surface on meLhanol decomposition. Total dehydrogenation occurs on the untreated surface, while that with S yields the partial dehydrogenation product, formaldehyde. From Johnson and Madix (1981).

The oxidation of methanol starts below 300° C. in the presence of a catalyst and quantities ranging up to 60 per cent of the total amount used in any experiment are decomposed. Not far from the oxidation temperature of the alcohol, formaldehyde undergoes decomposition into carbon monoxide and hydrogen. As much as 50 per cent of the formaldehyde which is formed may decompose in this way under certain conditions and ill the presence of certain catalysts. The oxidation of hydrogen to water... 

To overcome the objectionable reoxidation of formaldehyde and decomposition at the temperature of the reaction zone in the oxidation of methane, it has been proposed to react the formaldehyde as fast as formed with some substance to give a compound more stable under the conditions of the reaction and thus to increase the yields obtainable. It is claimed 101 that a reaction between the newly formed formaldehyde and annnonia to form a more stable compound, hexamethylene-tetramine, is possible under certain conditions, so that the formaldehyde is saved from destruction and can be obtained in a technically satisfactory yield. The hexamethylenetetramine is prepared by oxidizing methane with air in the presence of ammonia gas. A mixture consisting of six volumes of methane, twelve volumes of oxygen, and four volumes of ammonia gas is passed through a constricted metal tube which is heated at the constriction. The tube is made of such a metal as copper, silver, nickel, steel, iron, or alloys of iron with tin, zinc, aluminum, or silicon or of iron coated with one of these metals. Contact material to act as a catalyst when non-catalytic tubes are used in the form of wire or sheets of silver, copper, tin, or alloys may be introduced in the tube. At atmospheric pressure a tube temperature... 

HDPE can present some health hazard during its combustion, pyrolysis, or during thermocutting, when smoke, fumes or toxic decomposition products can be formed. Irritation of the skin, eyes, and mucous membranes of the nose and throat are possible. In some cases this irritation has been traced to traces of acrolein or formaldehyde from thermooxidative decomposition. However, other large-scale Are testing of foamed PE imder actual conditions did not reveal significant acrolein formation and demonstrated that PE presents no worse hazard than cellulosic materials. Still other studies indicate that maximum evolution of irritants occurs from smoldering combustion at 300-400°C. 

Tile bella iur of fomialdelivde. Solutions on distillation under various conditions of temperature and pressure indicates that the partial pi-essure of formaldehyde over these solutions Ls in reality the decomposition pres-sure of dissolved foimaldehyde hydrate-h AVitli the aid of this concept it Is possible to predict the bdiavior of aqueous formaldehyde solutions under various conditions and devise methods for the l eco en or imioval of formaldehyde from these systems Solutions containing components other than formaldehyde and water can prolialily be handled in a sunilar fashion, pro-vdded these components do not react with fomialdchyde under the conditioas stipulated. 

Anhydrous, monomeric formaldehyde is not available commercially. The pure, dry gas is relatively stable at 80—100°C but slowly polymerizes at lower temperatures. Traces of polar impurities such as acids, alkahes, and water greatly accelerate the polymerization. When Hquid formaldehyde is warmed to room temperature in a sealed ampul, it polymerizes rapidly with evolution of heat (63 kj /mol or 15.05 kcal/mol). Uncatalyzed decomposition is very slow below 300°C extrapolation of kinetic data (32) to 400°C indicates that the rate of decomposition is ca 0.44%/min at 101 kPa (1 atm). The main products ate CO and H2. Metals such as platinum (33), copper (34), and chromia and alumina (35) also catalyze the formation of methanol, methyl formate, formic acid, carbon dioxide, and methane. Trace levels of formaldehyde found in urban atmospheres are readily photo-oxidized to carbon dioxide the half-life ranges from 35—50 minutes (36). 

Most likely singlet oxygen is also responsible for the red chemiluminescence observed in the reaction of pyrogaHol with formaldehyde and hydrogen peroxide in aqueous alkaU (152). It is also involved in chemiluminescence from the decomposition of secondary dialkyl peroxides and hydroperoxides (153), although triplet carbonyl products appear to be the emitting species (132). 

A series of phosphorus- and bromine-containing FRs were synthesized and studied to understand their role, especially their combined effects. Thus, monocar-danyl phosphoric acid, its bromo derivatives and their formaldehyde condensates and crosslinked products [28,188] were prepared and their properties compared with analogous products made from phenol [28,189]. Table 14 gives the LOI values, char yields (Cy at 600°C), and thermal stability at 50% (T6o) decomposition. 

The reaction of benzoxazine in die presence of 2,6-xylenol does not occur until 135 C, presumably because die hydrogen-bonded intermediate depicted for the 2,4-xylenol reaction (Fig. 7.19) cannot occur. All three types of linkages are obtained in diis case. Para-para methylene-linked 2,6-xylenol dimers, obtained from the reaction of 2,6-xylenol with formaldehyde, formed in the decomposition of the benzoxazine (or with other by-products of that process) dominate. Possible side products from benzoxazine decomposition include formaldehyde and CH2=NH, either of which may provide the source of methylene linkages. Hie amount of ortho-para linkages formed by reaction of 2,6-xylenol with benzoxazine is low. Ortho-ortho methylene-linked products presumably form by a decomposition pathway from benzoxazine (as in Fig. 7.18). 

Figure 5. Cartoon models of the reaction of methanol with oxygen on Cu(llO). 1 A methanol molecule arrives from the gas phase onto the surface with islands of p(2xl) CuO (the open circles represent oxygen, cross-hatched are Cu). 2,3 Methanol diffuses on the surface in a weakly bound molecular state and reacts with a terminal oxygen atom, which deprotonates the molecule in 4 to form a terminal hydroxy group and a methoxy group. Another molecule can react with this to produce water, which desorbs (5-7). Panel 8 shows decomposition of the methoxy to produce a hydrogen atom (small filled circle) and formaldehyde (large filled circle), which desorbs in panel 9. The active site lost in panel 6 is proposed to be regenerated by the diffusion of the terminal Cu atom away from the island in panel 7.

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