Preparations in the absence of oxygen

Such one-step reactions are the exception rather than the rule. More commonly, it is necessary to carry out a series of successive reactions and procedures, such as refluxing, distilling, crystallization, filtration and washing in an inert atmosphere. The most evident way of doing this is to work in an inert-atmosphere filled glove box using conventional apparatus. This is both 

Reactions involving metals, either bulk or, more commonly, finely divided, are an entry point for organometallic complexes of transition metals. Examples of direct reaction of a metal are 

This process can be carried further, in which the product reacts with carbon monoxide in hexane in the presence of a mild alkali  

The product is a black crystalline material. The molecules consist of a tetrahedron of rhodium atoms, each rhodium atom being bonded to the other three rhodiums and to three CO ligands, [Rh(CO)3]4 (this compound will be the subject of discussion in Chapter 15). 

This same pattern was noted earlier, when describing the preparation of Cr complexes from chromates that, if at all possible, a ligand is also used as reducing agent. Other examples are the reaction of rhodium trichloride with triphenylphosphine in hot ethanol to give Wilkinson s compound, [RhCl(P(C6H5)3)3]  

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Determinations have been made of the solubility of lead linoleate prepared in the absence of oxygen and extracted with air-free water. Under these conditions, lead linoleate had a solubility of 0-002% at 25°C and the extract was corrosive when exposed to the air. When, however, the extraction was carried out in the presence of air, the resulting extract contained 0 07% solid material and was non-corrosive. It was concluded that in the presence of water and oxygen lead linoleate yielded soluble inhibitive degradation products. 

An important question, studied in considerable detail, is whether the oxidative cleavage of catechol and o-benzoquinone does or does not require molecular oxygen. Experiments under anaerobic conditions with the "copper reagent" prepared in the absence of oxygen yielded essentially the same amounts of 21 as the aerobic syntheses. The obvious conclusion is that catechol is stoichiometrically oxidized by a copper(II) species and molcular oxygen is not involved in the cleavage. The function of 0 is merely to reoxidize the copper(I) formed. 

Germanium monoxide [20619-16-3], GeO, can best be prepared in pure form by heating a mixture of Ge and Ge02, in the absence of oxygen. At temperatures above 7I0°C, GeO sublimes from the mixture and condenses as a glassy deposit in the cooler part of the reaction vessel. Germanium monoxide is stable at room temperature. 

Beryllium Nitride. BeryUium nitride [1304-54-7], Be N2, is prepared by the reaction of metaUic beryUium and ammonia gas at 1100°C. It is a white crystalline material melting at 2200°C with decomposition. The sublimation rate becomes appreciable in a vacuum at 2000°C. Be2N2 is rapidly oxidized by air at 600°C and like the carbide is hydrolyzed by moisture. The oxide forms on beryllium metal in air at elevated temperatures, but in the absence of oxygen, beryllium reacts with nitrogen to form the nitride. When hot pressing mixtures of beryUium nitride and sUicon nitride, Si N, at 1700°C, beryllium sUicon nitride [12265-44-0], BeSiN2, is obtained. BeSiN2 may have appHcation as a ceramic material. 

Copper Oxides. Coppet(I) oxide [1317-39-17 is a cubic or octahedral naturally occurring mineral known as cuprite [1308-76-5]. It is ted or reddish brown in color. Commercially prepared coppet(I) oxides vary in color from yellow to orange to ted to purple as particle size increases. Usually coppet(I) oxide is prepared by pytometaHutgical methods. It is prepared by heating copper powder in air above 1030°C or by blending coppet(II) oxide with carbon and heating to 750°C in an inert atmosphere. A particularly air-stable coppet(I) oxide is produced when a stoichiometric blend of coppet(II) oxide and copper powder ate heated to 800—900°C in the absence of oxygen. Lower temperatures can be used if ammonia is added to the gas stream (27-29). 

Viable methods of producing the metals from oxide ores have to siumount two problems. In the first place, reduction with carbon is not possible because of the formation of intractable carbides (p. 299), and even reduction with Na, Ca or Mg is unlikely to remove all the oxygen. In addition, the metals are extremely reactive at high temperatures and, unless prepared in the absence of air, will certainly be contaminated with oxygen and nitrogen. 

In the absence of oxygen, these thiolene-2-ones are rather stable and have been kept at 0°C for several months. 3-Hydroxythiophene, on the other hand, which has been prepared in low yield from 3-thio-phenemagnesium bromide in the same way as the 2-isomer, or through decarboxylation of 3-hydroxy-2-thiophenecarboxylic acid, "" is very unstable. Its IR spectrum indicates that it also exists as a tautomeric mixture largely in its enolic form. ... 

The same thing happens when alkyl halides are treated with silver in the presence of oxygen.41 The reaction with silver in the absence of oxygen is of course one of the methods used to prepare the stable triarylmethyl free radicals. 

NO was prepared by mixing 1 M NaNOj with 1 M HCl (1 1, v v) in an 02-free, bottle. The gas liberated from this was bubbled through oxygen-free distilled H2O, into which it dissolves readily in the absence of oxygen, for 2 hr prior to diluting the solution. At... 

The ion Cu" is extremely labile. Rate constants for the formation of maleate or fumarate complexes are =10 M s Ref. 281. It can be prepared in an acid perchlorate solution by reaction of Cu with a one-electron reducing agent such as Cr, or Eu Ref. 282. Although there is a marked tendency for disproportionation, solutions of Cu are metastable for hours in the absence of oxygen, particularly when concentrations of Cu(I) are low and the acidity is high. Espenson has capitalized on this to study the rates of reduction by Cu of some oxidants, particularly those of Co(III), Table 5.7 (see Prob. 6(c) Chap. 5). 

They presented the first synthesis of cobalt(III) cyclam in the absence of oxygen. Generally, for such a procedure, molecular oxygen is used to convert cobalt(II) to cobalt(III). However, because there are systems for which oxygen is undesirable, preparation of cobalt(III) cyclam from a refluxing mixture of tri(acetylacetonato)cobalt(III) and cyclam is a significant accomplishment. 

No special precautions are required to prepare material of this quality. However, since the loss of conductivity in samples of (TTF)(TCNQ) has been attributed to inclusion of impurities18 it is appropriate to use purified starting materials and distilled solvents and to perform the reaction in the absence of oxygen. Although the product is easy to prepare, the crystals are small and therefore not suitable for single-crystal measurements. 

One series of experiments was run at pH 8.2 to determine the effect of oxygen on solutions of the ferric complex. Because of the rapid second-order rate of bleaching at this pH it was necessary to prepare a fresh stock solution of the ferric complex for each point and to work as rapidly as possible. Even so, blanks under similar conditions but in the absence of oxygen showed that in some of the experiments [high iron (III), low mercaptoacetate] appreciable production of iron (II) had occurred by the time of mixing. In spite of this, these experiments provided useful data. 

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