Pyridine ammonia

Urea - formaldehyde polymers. Formalin and urea (usually in the molecular proportions of 3 2) condense in the presence of ammonia, pyridine or hexamine to give urea - formaldehyde polymers, known commercially as Bedle or Plaskon, and are widely used as moulding powdens. It is believed that the intermediate products in the condensation are methylol-urea and dimethylol-urea ... 

TiF is a colorless, very hygroscopic soHd and is classified as a soft fluorinating reagent (4), fluorinating chlorosilanes to fluorosilanes at 100°C. It also forms adducts, some of them quite stable, with ammonia, pyridine, and ethanol. TiF sublimes at 285.5°C, and melts at temperatures >400° C. It is soluble in water, alcohol, and pyridine, hydroly2ing in the former, and has a density of 2.79 g/mL. 

CuClO, and copper(II) perchlorate [13770-18-8] Cu(Cl04)2, form a number of complexes with ammonia, pyridine, and organic derivatives of these compounds. The copper perchlorate is an effective bum-rate accelerator for soHd propellants (39). 

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. 

Spectral studies at low temperatures enable us to broaden the number of test molecules for surface acidic sites and besides ammonia pyridine and nitriles, to use CO, NO and that do not adsorb at 300 K. 

A1C13, or S02 in an inert solvent cause colour changes in indicators similar to those produced by hydrochloric acid, and these changes are reversed by bases so that titrations can be carried out. Compounds of the type of BF3 are usually described as Lewis acids or electron acceptors. The Lewis bases (e.g. ammonia, pyridine) are virtually identical with the Bransted-Lowry bases. The great disadvantage of the Lewis definition of acids is that, unlike proton-transfer reactions, it is incapable of general quantitative treatment. 

Acidity of both zeolites was investigated by adsorption of ammonia, pyridine, d3-acetonitrile and pivalonitrile ((CH3)3CCN) used as probe molecules followed by FTIR spectroscopy. All samples were activated in a form of self-supporting wafers at 450 °C or 550 °C under vacuum for 1 h prior to the adsorption of probe molecules. 

SSZ-35 the reactions would be influenced by the presence of very strong Lewis sites. Quantitative sorption of ammonia, pyridine and d3-acetonitrile in both zeolites showed that the real number of acidic groups was close to values, derived form the number of aluminum atoms (taken from AAS analysis) in the idealized unit cell. Obtained values are 1.1 H+/u.c. for SSZ-33 with idealized unit cell composition H2.9[Al2.9Si53.iOii2] (plus 1.3 Lewis sites per u.c.) and 0.3 H+/u.c. for SSZ-35 with ideal formula Ho.4[Alo.4Sii5 6032] (plus 0.05 Lewis sites per u.c.). 

As has already been mentioned, boron halides are electron-deficient molecules. As a result, they tend to act as strong Lewis acids by accepting electron pairs from many types of Lewis bases to form stable acid-base adducts. Electron donors such as ammonia, pyridine, amines, ethers, and many other types of compounds form stable adducts. In behaving as strong Lewis acids, the boron halides act as acid catalysts for several important types of organic reactions (see Chapter 9). 

Similar conclusions are also reached for the magnetic shielding of atoms, as revealed by a detailed study of a series of amines, nitriles, ammonia, pyridine, pyra-zine, pyrimidine, and pyridazine [119]. Their local diamagnetic shielding is virtually... 

Dichloro-dipyridino-palladium, [Pd py2Cl2]. is produced by the addition of pyridine to an aqueous solution of palladous chloride or potassium chloropalladite. A red precipitate is first obtained, which dissolves on heating with excess of pyridine. From the liquid the substance is precipitated on the addition of concentrated hydrochloric acid as a bright yellow crystalline powder. If heated with ammonia, pyridine is eliminated and dichloro-diammino-palladium formed.2... 

Tellurium Halides. Tellurium forms the dihalides TeCl and TeBi, but not Tel2. However, it forms tetrahalides with all four halogens. Tellurium decafluoride [53214-07-6] and hexafluoride can also be prepared. No monohalide, Te2X2, is believed to exist. Tellurium does not form well-defined oxyhalides as do sulfur and selenium. The tellurium halides show varying tendencies to form complexes and addition compounds with nitrogen compounds such as ammonia, pyridine, simple and substituted thioureas and anilines, and ethylenediamine, as well as sulfur trioxide and the chlorides of other elements. 

Combinations of Bi203 and Mo03, promoted by P2Os at a constant P/Mo ratio (0.2) were studied over a full composition range by Ai and Ikawa [6], Acidity (and basicity) were measured directly by adsorption of compounds like ammonia, pyridine and acetic acid. The effect of the Bi/Mo ratio on the acidity (Fig. 14) parallels the effect on the overall butene oxidation activity [presented in Fig. 5, Sect. 2.3.2(a)(i)]. 

The experiments with reversible poisoning of alumina by small amounts of bases like ammonia, pyridine or piperidine revealed [8,137,142,145, 146] relatively small decreases of dehydration activity, in contrast to isomerisation activity which was fully supressed. It was concluded that the dehydration requires only moderately strong acidic sites on which weak bases are not adsorbed, and that, therefore, Lewis-type sites do not play an important role with alumina. However, pyridine stops the dehydration of tert-butanol on silica—alumina [8]. Later, poisoning experiments with acetic acid [143] and tetracyanoethylene [8] have shown the importance of basic sites for ether formation, but, surprisingly, the formation of olefins was unaffected. 

Gallium(III) bromide is a hygroscopic, white solid which sublimes readily and melts at 122.5° to a covalent, dimeric liquid. The solid is ionic and its electrical conductivity at the melting point is twenty-three times that of the liquid.5 The vapor pressure of the liquid at T°K is given by the equation log p(mm.) = 8.554 — 3129/T and the heat of dissociation of the dimer in the gas phase is 18.5 kcal./mol.3 At 125° the liquid has the following properties 5,6 density, 3.1076 dynamic viscosity, 2.780 c.p. surface tension, 34.8 dynes/cm. and specific conductivity, 7.2 X 10-7 ohm-1 cm.-1 Gallium(III) bromide readily hydrolyzes in water and forms addition compounds with ligands such as ammonia, pyridine, and phosphorus oxychloride. 

Infrared spectroscopic studies regarding the adsorption of pyridine on both anatase and rutile have been reported (136, 176, 194, 216,217). Hydrogen-bonded pyridine is readily desorbed on pumping at room temperature, whereas pyridine held by coordinatively unsaturated Ti4+ ions is thermally stable up to approximately 400°C. As ammonia, pyridine forms two distinct coordinately held species (176, 217) indicating the existence of two types of Lewis acid sites, which should correspond to Ti4+ ions in different stereochemical environments. According to Primet et al. (176), the more stable species is chemisorbed on type... 

Early poisoning experiments using nitrogen bases such as ammonia, pyridine, and piperdine have shown that the secondary isomerization of the primary ole-finic products can be completely suppressed, whereas the dehydration activity of the alumina catalyst was only slightly influenced by these poisons (30, 31,341-344). This is a typical example of selective poisoning, where a consecutive reac-... 

The same authors (140) then carried out a number of experiments where the catalyst pretreatment conditions were varied and reagents were added to the reaction mixture (i.e., ammonia, pyridine, and CO) in order to elucidate the type of active site. Rather surprisingly, it was concluded that... 

Desorption of water often converts Bronsted to Lewis acids, and readsorption of water can restore Bronsted acidity. Probe molecules, such as ammonia, pyridine, etc., are used to evaluate Bronsted and Lewis acidity. These compounds may contain water as an impurity, however. Water produced by reduction of metal oxides can also be readsorbed on acid sites. Probe molecules can in some cases react on surface acid sites, giving misleading information on the nature of the original site. Acidity, and accessibility, of hydroxyl groups or adsorbed water on zeolites and acidic oxides can vary widely. Study of adsorbed nitrogen bases is very useful in characterization of surface acid sites, but potential problems in the use of these probes should be kept in mind. 

The addition of a donor base such as ammonia, pyridine etc., favours the reaction both by neutralizing the mineral acidity and by stabilization of the coppcr(U) Oxidam complex, Cu(OR)Cl, by coordination. 

A number of substituted benzenes, naphthalenes, indans, pyridmes, and indoles form arene(tricarbonyl)chromium complexes upon thermolysis under an inert atmosphere, usually in a high boiling ether, or by irradiation of the arenes in the presence of chromium hexacarbonyl. The complexes are relatively air-stable and can usually be stored for long periods in the absence of light. Somewhat milder conditions can be used by transfer of the chromium tricarbonyl group from preformed naphthalene(tricarbonyl)chromium, tris(L)tricarbonyl chromium (L = acetonitrile, ammonia, pyridine), or tricarbonyl( -l-methylpyrrole)chromium. Enan-tiomerically pure arene(tricarbonyl)chromium complexes having two different substituents, either ortho or meta can be prepared conveniently by classical resolution of racemic... 

The acid-base properties of V2O5/7-AI2O3 catalysts prepared by the impregnation method have been characterized by ammonia, pyridine and sulfur dioxide adsorption microcalorimetry. Sulfur dioxide adsorption made it possible to differentiate a vanadate layer from free alumina. 

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