Formaldehyde, HCHO

Wet-chemical analysis and optical methods have been used to determine the abundance of formaldehyde in ambient air. Table 4-9 shows mixing ratios observed at various locations. The highest values are associated with urban air, especially under conditions of photochemical smog. Maximum values may then reach 70-100 ppbv. Mixing ratios in rural areas are of the order of a few ppbv, and still lower values are found in marine air masses. 

Lowe and Schmidt (1983) have measured formaldehyde over the Atlantic Ocean as a function of latitude. Their results are shown in Fig. 4-6. In the region 33°S-40°N the data scatter around a mean mixing ratio of wn(HCHO) = 0.22 ppbv. Further northward they decline. The lifetime of formaldehyde due to photodecomposition by sunlight is about 5 h at midlatitudes, and 15 h when averaged over a full day (Warneck et al., 1978). In addition, formaldehyde reacts with OH. Where the oxidation of methane is the sole source, formaldehyde mixing ratios are expected to be in steady state with methane [dm(HCHO)/dr = 0]  

Altshuller and McPherson Urban air Los Angeles, California 150 (Highest maximum) 

Kuwata et al. (1983) Osaka, Japan 23-71 (daily maximum) 1.6-8.5 (34 Highest 

Platt et al. (1979), Platt Rural air Jiilich, Federal Republic of 0.1-6.5 

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Physical properties. All colourless. Formaldehyde, HCHO, is a gas, and only its aqueous solution, which has a characteristic pungent odour, is considered metaformaldehyde or trioxymethylene , (CH20)3, is a solid polymer, insoluble in water and ethanol. 

Formaldehyde, HCHO, is a primary and necessary constituent of the first five synthetic adhesives in the listing. It is a simple organic chemical first identified during the latter half of the 1800s. Its irritating and toxic odor and preservative properties were known from the time of its early development. It is a ubiquitous chemical, formed naturally in small quantities by every process of incomplete combustion as well as in normal biologic processes. The human body has a natural formaldehyde level of about 3 lg/g, ie, 3 parts per million (ppm) in the blood at all times. 

Formaldehyde HCHO Acetylaldehyde CH3CHO Other aldehydes RCHO Acids... 

Sensitizer A sensitizer is defined by OSHA as "a chemical that causes a substantial proportion of exposed people or animals to develop an allergic reaction in normal tissue after repeated exposure to the chemical." The condition of being sensitized to a chemical is also called chemical hypersensitivity. Certain chemicals have no immediate health effect. But if you are exposed to them several times, they can make you allergic or sensitive to other chemicals. A classic example is formaldehyde (HCHO). Typical reactions to sensitizers can include skin disorders such as eczema. When working with sensitizers, always use proper protective equipment such as gloves, respirators, etc. Once you are sensitized to a particular chemical, even minute amounts will cause symptoms. Sensitization is usually a lifelong effect. 

Balance the half-reaction for the conversion of formaldehyde, HCHO, to formic acid, HCOOH. 

Write the complete Lewis structure for each of the following compounds (a) formaldehyde, HCHO, which as its aqueous solution formalin is used to preserve biological specimens (b) methanol, CH3OH, the toxic compound also called wood alcohol (c) glycine, H2C(NH2)COOH, the simplest of the amino acids, the building blocks of proteins. 

Typical reaction products of NO removal in non-thermal plasma in the presence of propylene, predicted by the model in Martin et al. and Dorai and Kushner [86,88], include formaldehyde (HCHO), acetaldehyde (CH3CHO) methyl oxirane (C3H60), gly-coxal (CHO-CHO), methyl nitrite (CH3ONO), methyl nitrate (CH30N02), and 2-nitroso ethanal (ONCH2CHO). 

Looking back at Table 4.4 the anaerobic cyclic steady state is from the first product of C0(C02) reduction, formaldehyde (HCHO), to [CH2OH] . This step requires a kinetic pathway in redox potential from -0.2 to -0.6 V versus the H2/H+ potential at pH 7, where sulfur is the oxidised waste ... 

The 7i bonding molecular orbital of formaldehyde (HCHO). The electron pair of the n bond occupies both lobes. 

Figure 3.1 Two essential steps of chemical reaction of formaldehyde (HCHO) with nucleic acid exemplified by adenine that are similar to formaldehyde-protein reactions, (a) Addition reaction as the first step, resulting in a methylol derivative, methylol adenylic acid (b) Second step is a condensation reaction, a stable product methylene-bis-adenylic acid is derived between the methylol derivative and another adenine. Reproduced with permission from Shi et al.,AIMM 2001 9 107-116. 

The photooxidation of acrylonitrile by hydroxyl radicals in the presence of nitric oxide has been observed to yield formaldehyde (HCHO) and formyl cyanide (HCOCN) (Hashimoto et al. 1984). 

However, if you link the hydroxyl group with the methane molecule rather than the ethane, you get the potentially toxic chemical called methyl alcohol, or wood spirit. Similarly, if you add what s called an aldehyde group (-CHO) instead of the hydroxyl group, you will get one of a variety of chemicals called aldehydes, of which a common one is the gas formaldehyde (HCHO), widely used in the manufacture of plastics and glues. This gas can be an irritant and potentially dangerous if inhaled. 

CH00CH3)t carbon dioxide (C02>. formic acid (HCOOH), and formaldehyde (HCHO) are detected in the solution during the oxidation of methanol on platinum in sulfiiric add. While these are stable and detached spedes, spedes that are unstable or adsorbed on the electrode surface are also expected to be formed. 

This is known as the indirect mechanism because it requires the removal of CO. The direct mechanism goes through formaldehyde (HCHO) and formic acid (HCO2H) intermediafes and allows for desorption at each step. 

Dehydrogenation. The removal of one or more hydrogen atoms from a molecule by chemical means, as in the conversion of alcohols to aldehydes. For example, methanol (CH3OH) can be oxidized to formaldehyde (HCHO) plus H2. ... 

Electroless Deposition of Copper. The basic ideas of the mixed-potential theory were tested by Paunovic (10) for the case of electroless copper deposition from a cupric sulfate solution containing ethylenediaminetetraacetic acid (EDTA) as a complexing agent and formaldehyde (HCHO) as the reducing agent (Red). The test involved a comparison between direct experimental values for and the rate of deposition with those derived theoretically from the current-potential curves for partial reactions on the basis of the mixed-potential theory. 

Formaldehyde (HCHO) is a colorless gas with a pungent odor. Formaldehyde has found wide industrial usage as a fungicide and germicide, and in disinfectants and embalming fluids. The serious sources of indoor airborne formaldehyde are furnimre, floor underlayment insulation, and environmental tobacco smoke. Urea formaldehyde (UF) is mixed with adhesives to bond veneers, particles, and fibers. It has been identified as a potential hazardous source. 

Benning, L and A. Wahner, Measurements of Atmospheric Formaldehyde (HCHO) and Acetaldehyde (CH3CHO) during POPCORN 1994 Using 2,4-DNPH Coated Silica Cartridges, J. Atmos. Chem., 31, 105-117 (1998),... 

Formaldehyde (HCHO) FORM Toluene-hydroxyl radical adduct T02... 

Similar to several other trace species, formaldehyde (HCHO) occurs in elevated concentrations as a result of pollution in the lower troposphere. Formaldehyde is generated during the oxidation of hydrocabons in copious amounts. However, as it is photolysed and reacts with OH, it has a relatively short tropospheric lifetime. The observation of formaldehyde from GOME over industrial and biomass burning regions has been discussed by Pemer et al. (1998) and Burrows et al. (1999). Thomas et al. (1998) also observed formaldehyde over Borneo using GOME data. 

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