Mo compounds

Although molybdenum is an essential element, excess levels can have deleterious effects. The LD q and TLV values of the most common Mo compounds are Hsted in Table 3 (63,64). In general the toxicity of Mo compounds is considered to be low. For example, M0S2 has been found to be virtually nontoxic even at high levels. Certain Mo compounds such as MoCl and Mo(CO), have higher toxicity because of the chemical nature and reactivity of these compounds rather than the Mo content. Supplementary dietary Cu ", thiosulfate, methionine, and cysteine have been shown to be effective in alleviating Mo toxicity in animals. 

In 1826 J. J. Berzelius found that acidification of solutions containing both molybdate and phosphate produced a yellow crystalline precipitate. This was the first example of a heteropolyanion and it actually contains the phos-phomolybdate ion, [PMoi204o] , which can be used in the quantitative estimation of phosphate. Since its discovery a host of other heteropolyanions have been prepared, mostly with molybdenum and tungsten but with more than 50 different heteroatoms, which include many non-metals and most transition metals — often in more than one oxidation state. Unless the heteroatom contributes to the colour, the heteropoly-molybdates and -tungstates are generally of varying shades of yellow. The free acids and the salts of small cations are extremely soluble in water but the salts of large cations such as Cs, Ba" and Pb" are usually insoluble. The solid salts are noticeably more stable thermally than are the salts of isopolyanions. Heteropoly compounds have been applied extensively as catalysts in the petrochemicals industry, as precipitants for numerous dyes with which they form lakes and, in the case of the Mo compounds, as flame retardants. 

At temperatures above 45°C, however, (NRj MOs compounds decompose yielding gaseous ammonia, NH3, and oxygen as well as tantalum or niobium oxides ... 

The osmium MO compounds are much more numerous and have greater stability. 

The products of this first stage of the reaction, cis Mo or Cr(CO)4LX and cis Mn or Re(CO)4LX undergo further substitution. The Mn, Re compounds behave according to first-order kinetics while the Cr, Mo compounds show second-order kinetics to form trans Cr(CO)4L2 or cwMo(CO)4L2, rate coefficients increasing this time as expected, with the basicity of the entering ligand L. 

Hexavalent Mo compounds absorbed appreciably, but not disulfide compounds (10, 13)... 

The reactions 11 and 12 of the optically active Mo compounds 13 follow the typical pattern of organic S 2 reactions. Racemization occurs if the optically active compounds are treated with nucleophiles that are identical with the leaving groups. Better nucleophiles lead to a Walden inversion. 

Ternary mixtures show enhanced antifriction and antiwear properties of Mo compounds (Lin, 1995). 

It is deduced that competitive adsorption between ZDDP and MoDTC onto the surface occurred during the run, because Mo concentration on the surface with ZDDP + MoDTC oil was lower than that obtained with the oil containing MoDTC alone. The adsorption of the additive on a surface results in formation of a film composed of the decomposition compounds or reaction compounds of the additives with the metal surface. The decline in the Zn/Mo atomic concentration ratio in the film composition with test time indicates that the decomposition products of ZDDP, which had a high coefficient of friction, were preferentially formed and subsequently, Mo compounds were formed. Similarly, an increase in the concentration of MoS2 with time was also observed. A necessary condition for the production of an effective surface film for reducing friction is the previous formation of the compounds derived from ZDDP. 

The stability of metal alkylidene (carbene) complexes and the corresponding metallacycles can be dependent on various factors, but it is worth noting that the kind of metal, the metal oxidation state and the ligands surrounding the metal are considered to be of essential significance. Although stable metal carbene complexes are usually obtained from W and Mo compounds whereas metallacycles are obtained from Ti compounds, systems have been found in which both the metal alkylidene complex and its precursor metallacyclobutane can be detected at lowered temperature by NMR spectroscopy [45]. 

Alcohols may be oxidized in a similar way. However, these reactions strongly resemble those reported for Cr molecular sieves, and a small concentration of Cr in solution may well account for most of the observations of catalysis. Binary molybdenum-chromium oxides supported on alumina have been used in the autoxidation of cyclohexene with 02 and r-BuOOH as an initiator (62). This is a complex reaction in which uncatalyzed and Cr-catalyzed oxidation combine to yield 2-cyclohexen-l-one, 2-cyclohexen-l-ol, and 2-cyclohexenyl hydroperoxide the Mo compound can use the hydroperoxide formed in situ as an oxidant for the epoxidation of cyclohexene. Although much lower oxygen consumption was observed for the reaction filtrate than for the suspension, it is unclear how the Cr is held by the oxide. 

Molybdenum. Molybdenum can be analyzed by P CAM 173 for total Mo, by S-193 (12) for soluble Mo, or by S-376 for insoluble Mo. The standard nitric wet ashing used in P CAM 173 does not distinghish between soluble and insoluble Mo which have OSHA standards of 5 mg/cu m and 15 mg/cu m. Nitric acid digestion may not dissolve some insoluble Mo that require nitric/perchloric acid or base/nitric acid depending on the solubility properties. Soluble Mo compounds are hot water leached from the cellulose membrane filter used in all three methods. A fuel-rich air/acetylene flame used in P CAM 173 is replaced by an oxidizing nitrous oxide/acetylene flame to achieve total atomization of Mo as detected at 313.3 nm. Aluminum and traces of acid enhance the Mo flame response therefore, 400 ppm A1 is added to the final solution of both S-193 and S-376 and 0.1 N nitric acid is added to the water leach-soluble Mo final solution, S-193. 

---