Formaldehyde alternatives

If the effective temperature of our defined system is less than the universal radiation background temperature of 2.7 K, transitions between the two levels can be observed in absorption. This is the case with interstellar formaldehyde. Alternatively absorption can be observed against the continuum radiation from a nearby bright source. Spontaneous emission will always occur provided the upper of the two levels is populated, and can be observed if the populations are different. There are, in addition, examples of the exceptional situation in which N2 > N the result of this population inversion is that stimulated emission dominates, and maser emission is observed. Interstellar OH and SiO provide diatomic examples of this unusual situation, as also does interstellar H2O we shall describe the results for OH later in this chapter. Departures from local thermodynamic equilibrium are very common, and the concept of temperature in interstellar gas clouds is not simple this is a major part of astrophysics which is, however, beyond the scope of this book. 

In the fluorometric method I, the NADH produced is monitored spectrofluorometrically at an excitation wavelength (Xex nm and an emission wavelength ) of 467 nm. The fluorescence intensity is proportional to the concentration of formaldehyde. Alternatively, the following coupled reaction can be used for more sensitive analysis of formaldehyde in the ppb concentrations ... 

Place 3 3oz packets of Mildewcide into a 1L flask with an electric heating mantle and cork in the neck connected to a gas bubbler immersed in at least 550mL of distilled water. Heat the paraformaldehyde (what is in the Mildewcide) to between 180-200C (a temp, regulator is absolutely necessary for this step or use a silicone oil bath). The paraformaldehyde will depolymerize making formaldehyde gas in about 91% yield. Alternatively, the gas can be bubbled through the Ammonia solution directly (only for the brave ). If the Formaldehyde solution will not be used immedi-... 

Rhoda.mines, Rhodamines are commercially the most important arninoxanthenes. If phthalic anhydride is used in place of formaldehyde in the above condensation reaction with y -dialkylarninophenol, a triphenyknethane analogue, 9-phenylxanthene, is produced. Historically, these have been called rhodamines. Rhodamine B (Basic Violet 10, Cl45170) (17) is usually manufactured by the condensation of two moles of y -diethylaminophenol with phthahc anhydride (24). An alternative route is the reaction of diethylamine with fluorescein dichloride [630-88-6] (3,6-dichlorofluoran) (18) under pressure. 

Butanediol. 1,4-Butanediol [110-63-4] made from formaldehyde and acetylene, is a significant market for formaldehyde representing 11% of its demand (115). It is used to produce tetrahydrofuran (THF), which is used for polyurethane elastomers y-butyrolactone, which is used to make various pyrroHdinone derivatives poly(butylene terephthalate) (PBT), which is an engineering plastic and polyurethanes. Formaldehyde growth in the acetylenic chemicals market is threatened by alternative processes to produce 1,4-butanediol not requiring formaldehyde as a raw material (140) (see Acetylene-derived chemicals). 

The in situ process is simpler because it requires less material handling (35) however, this process has been used only for resole resins. When phenol is used, the reaction system is initially one-phase alkylated phenols and bisphenol A present special problems. As the reaction with formaldehyde progresses at 80—100°C, the resin becomes water-insoluble and phase separation takes place. Catalysts such as hexa produce an early phase separation, whereas NaOH-based resins retain water solubiUty to a higher molecular weight. If the reaction medium contains a protective coUoid at phase separation, a resin-in-water dispersion forms. Alternatively, the protective coUoid can be added later in the reaction sequence, in which case the reaction mass may temporarily be a water-in-resin dispersion. The protective coUoid serves to assist particle formation and stabUizes the final particles against coalescence. Some examples of protective coUoids are poly(vinyl alcohol), gum arabic, and hydroxyethjlceUulose. 

Melamine—formaldehyde resins may be used in paper which contacts aqueous and fatty foods according to 21 CFR 121.181.30. However, because a lower PEL has been estabUshed by OSHA, some mills are looking for alternatives. Approaches toward achieving lower formaldehyde levels in the resins have been reported (66,67) the efficacy of these systems needs to be estabUshed. Although alternative resins are available, significant changes in the papermaking operation would be required in order for them to be used effectively. 

Key intermediates in the industrial preparation of both nicotinamide and nicotinic acid are alkyl pyridines (Fig. 1). 2-Meth5l-5-ethylpyridine (6) is prepared in ahquid-phase process from acetaldehyde. Also, a synthesis starting from ethylene has been reported. Alternatively, 3-methylpyridine (7) can be used as starting material for the synthesis of nicotinamide and nicotinic acid and it is derived industrially from acetaldehyde, formaldehyde (qv), and ammonia. Pyridine is the principal product from this route and 3-methylpyridine is obtained as a by-product. Despite this and largely due to the large amount of pyridine produced by this technology, the majority of the 3-methylpyridine feedstock is prepared in this fashion. 

Many alternatives to nitrocellulose lacquers for top coats have been investigated and some are used commercially. Especially for lower cost furniture exposed to hard use such as motel and institutional furniture, alkyd—urea top coats are used. Urea—formaldehyde resins, in contrast to... 

An alternative approach to the production of thermally stable polyoxy-methylenes was made by chemists of the Celanese Corporation of America and the commercial products were marketed as Celcon. Hostaform and Duracon. The principle of thermal stability in this case is the copolymerisation of formaldehyde with a second monomer which is a cyclic ether of the general form shown in Figure 19.3 (I). 

The principal application of melamine-formaldehyde moulding compositions is for the manufacture of tableware, largely because of their wide colour range, surface hardness and stain resistance. The stain resistance does, however, leave something to be desired and one aim of current research is to discover alternative materials superior in this respect. Cellulose-filled compositions also find a small outlet for trays, clock cases and radio cabinets and other purposes. The mineral-filled powders are used in electrical applications and knobs and handles for kitchen utensils. 

A number of alternative curing agents to formaldehyde are known but once again have achieved no commercial significance. They include isocyanates, benzoquinone and chromium salts. 

Where resorcinol adhesives are not suitable, resins can be prepared from modified resorcinol [128], Characteristic of these types of resins arc those used for tyre cord adhesives, in which a pure resorcinol-formaldehyde resin is used, or alternatively, alkyl resorcinol or oil-soluble resins suitable for rubber compounding are obtained by prereaction of resorcinol with fatty acids in the presence of sulfuric acid at high temperature followed by reaction with formaldehyde. Worldwide more than 90% of resorcinol adhesives are used as cold-setting wood adhesives. The other most notable application is as tyre cord adhesives, which constitutes less than 5% of the total use. 

An alternative copolymerization is illustrated by the method of Blasius. In this preparation, a phenol-formaldehyde (novolac) type system is formed. Monobenzo-18-crown-6, for example, is treated with a phenol (or alkylated aromatic like xylene) and formaldehyde in the presence of acid. As expected for this type of reaction, a highly crosslinked resin results. The method is illustrated in Eq. (6.23). It should also be noted that the additional aromatic can be left out and a crown-formaldehyde copolymer can be prepared in analogy to (6.22). ... 

An alternative route to acrylic esters is via a (3-propiolactone intermediate. The lactone is obtained by the reaction of formaldehyde and ketene, a dehydration product of acetic acid ... 

A subclass of lyases, involved in amino acid metabolism, utilizes pyridoxal 5-phosphate (PLP, 3-hydroxy-2-methyl-5-[(phosphonooxy)methyl]-4-pyridinecarbaldehyde) as a cofactor for imine/ enamine-type activation. These enzymes are not only an alternative to standard fermentation technology, but also offer a potential entry to nonnatural amino acids. Serine hydroxymethyl-tansferase (SHMT EC 2.1.2.1.) combines glycine as the donor with (tetrahydrofolate activated) formaldehyde to L-serine in an economic yield40, but will also accept a range of other aldehydes to provide /i-hydroxy-a-amino acids with a high degree of both absolute and relative stereochemical control in favor of the L-erythro isomers41. 

Since a small amount of water is always present in novolac resins, it has also been suggested that some decomposition of HMTA proceeds by hydrolysis, leading to the elimination of formaldehyde and amino-methylol compounds (Fig. 7.15).42 Phenols can react with the formaldehyde elimination product to extend the novolac chain or form methylene-bridged crosslinks. Alternatively, phenol can react with amino-methylol intermediates in combination with formaldehyde to produce ortho-or para-hydroxybenzylamines (i.e., Mannich-type reactions). 

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