Ammonia solvent

Some studies seeking preferred conditions for this reaction have been reported. Optimum yields of 1-ethoxy-1-propyne and 1-ethoxy-l-butyne are found when the product is worked up before allowing the ammonia solvent to evaporate, as the product evidently volatilizes with the ammonia. An experiment with 1-ethoxy-1-propyne showed a marked increase in yield when ammonia predried over calcium hydride was used instead of ammonia directly from the cylinder. A twofold excess of ethyl bromide is required to obtain a good yield of l-ethoxy-l-but5me, since elimination apparently competes with alkylation in this case. 

Typical solvent system reactions are summarized below together with the analogous reactions from the liquid ammonia solvent system ... 

Unfortunately, investigators have classified a component as a /3-inhibitor if it was acidic and migrated at an appropriate Rf in the 2-propanol-ammonia solvent system. Robinson and Wareing 124)... 

Decide on the basis of the information in Table 10.3 whether carbonic acid is a strong or weak acid in liquid ammonia solvent. Explain your answer. 

Isolation of the active component is carried out chro-matographically. Roth et al.9 used a magnesol (magnesium silicate) column to absorb colored impurities, followed by a Darco G-60 activated carbon column to eliminate sodium formate and inorganics. Elution with an alcohol/ammonia solvent was followed by rechromatographing in magnesol. 

FIGURE 14.9 Performance of short column ultrahigh pressure nano LC system at 10 /rL/min for the separation of tranylcypromine sulfate, perphenazine, and their impurities. Nano LC may be operated at 10 times optimum column flow rate and achieve ultrahigh throughput and reproducibility. Short column (3 cm x 150 /mi inner diameter) was packed with 1.8 /im C18 particles. Solvent A was water with 0.4% ammonia solvent B was acetonitrile with 0.4% ammonia. Gradient 0 to 1 min, 3 to 10% B 1 to 1.3 min, 10 to 35% B, 1.3 to 3.5 min, 35 to 90% B held at 90% B through 4.9 min and then returned to 3% B. Column head pressure was 7200 psi. 

It should be pointed out that even in the case of complete evaporation of the ammonia solvent the alkynylide still contains ammonia, which is rather tightly bound. It is probably this NH3 that stabilizes LiCaCH in the same manner as do H2NCHjCTl2NH2 and TMEDA (compare exp. 6). 

Platinum(II) acetylide complexes are best prepared using Na or K acetylide in liquid ammonia solvent (equation 157).454,455 Sodium dicyanomethanide can also be used to prepare platinum(II) complexes of this anion (equation 158).456... 

Detailed drawings of low-temperature cells, including cells for liquid ammonia solvent [8], have been published [27]. 

The only isomer that has been studied is 4-(26). The polymerization was effected in either ammonia solvent or in a solvent-free system.57 An anionic mechanism was proposed, and molecular weights were in the range of 10,000 to 260,000. As expected, higher current densities led to lower average molecular weights. 

An estimate of the volume of solvent added to the hydrocarbon mixture was obtained by calculating the difference in the liquid level before and after gas addition, which is approximately equal to the volume of gas dissolved in the liquid phase. This value is added to the volume above the liquid interface to obtain the total solvent volume added to the system. The ratio of ethylene/ammonia solvent mixture added to the volume of butadiene/butene solution was approximately 5 1. 

Tie lines of the system can be generated from the equilibrium compositions for each run and selectivities computed. The results of measurements obtained for the 5% by volume of ammonia/ethylene are represented in the binodal diagram in Fig. 3. Butene is represented as the distributed component between the solvent phase and the butadiene-rich phase. The ammonia-solvent gas mixture was considered to behave as a pseudo-solvent of fixed composition. The ratio of the integrated peaks for butene(i) and butadiene(j) was used to compute the selectivity, B (beta), defined on a solvent-free basis, as ... 

Representative results are shown in Table II and III for ethylene and ethylene/ammonia and ethane and ethane/ammonia solvent mixtures. Since our detection capability was limited to hydrocarbons gases only, ammonia could not be directly measured in either phase. However, the selectivity as defined in Eqn. 2 can be considered as a measure of the ratio of the distributed components only hence, independent of the absolute concentration of the solvent components. 

Solvent to feed ratios as well as the effect of ammonia concentration in the solvent were independently varied to match the experimental data. The effect of increasing ammonia concentration at constant pressure and temperature in both ethylene/ammonia and ethane/ammonia solvent mixtures are shown in Table V. 

By responding to fumes in cooking areas, car parks, laboratories and similar places, gas sensors can be used to control ventilation fans. In industrial situations the sensor can monitor concentrations of carbon monoxide, ammonia, solvent vapours, hydrocarbon gases, ozone etc., and because of the growing consciousness of environmental pollution and the safety aspects of industrial processes the applications will multiply. 

A normal alkene is not reduced under the conditions of the Birch reduction because its pi antibonding MO is too high in energy for an electron from a sodium atom to be readily added to it. However, as shown in the following example, a carbon-carbon double bond that is conjugated with a carbonyl group is readily reduced by lithium or sodium metal in liquid ammonia solvent, without any added alcohol. 

The mechanism for this reaction is slightly different from that presented previously for the reduction of benzene. First an electron is added to the pi antibonding MO to produce a radical anion. Because there is no alcohol to protonate this anion, a second electron is then added to produce a dianion. The dianion is a strong enough base to remove a proton from the ammonia solvent, producing an enolate anion. The enolate anion is stable to the reaction conditions until acid is added to work up the reaction. 

Again, the mechanism proceeds by initial formation of a radical anion, which is then protonated by the ammonia solvent. The resulting radical accepts another electron from the sodium to produce an anion that has the bulky alkyl groups in a trans orientation. This anion removes a proton from another ammonia molecule to give the final product. 

The metal-ammonia reduction proceeds by addition of an electron to the alkyne to form a radical anion, followed by protonation to give a neutral radical. Protons are provided by the ammonia solvent or by an alcohol added as a cosolvent. Addition of another electron, followed by another proton, gives the product. 

Lithium, Li Reduces alkynes in liquid ammonia solvent to yield trans alkenes (Section 8.5). 

Chain transfer to the ammonia solvent by deprotonation of the carbanion is common in such systems [73] ... 

There is substantial chain transfer to the ammonia solvent and some to water that is likely to be present as a trace impurity. Transfer may occur from the covalent species or either kind of ion pair or a combination of these, but the transfer rates are of the same algebraic form and so can be lumped without loss in accuracy. The rates are... 

O .. which abstracts another proton from ammonia solvent to yield the final trans alkene product. 

It has been noted elsewhere that the order of addition of reagents is the most important single variable to influence product distribution. A procedure which is convenient and normally reliable is based on the addition of small pieces of metal to a mixture of substrate, ammonia, solvent and (if appropriate) alcohol at less than -70 °C until the blue colour persists for a reasonable period (approximately 10 min). For less reactive substrates, lithium should be used and the addition of the alcohol delayed so that a higher concentration of metal is maintained during the reduction process. Quenching is best effected by 1,3-penta-diene (or similar substance), followed either by ammonium chloride or another electrophile. In reactions where in situ alkylations are performed these are best carried out on lithium derivatives, so in cases where other metals have been used for reduction carefully dried lithium bromide is added before the electrophile. 

Most of the lipids of the neutral fraction were eluted at the solvent front when the chloroform/methanol/water solvent system, which is suitable for the separation of the acidic fraction, was used. We then tried solvent systems which can separate more hydrophobic lipids. Using the hexane/ ethyl acetate/ethanol/0.1% aqueous ammonia solvent system, we could separate phospholipids (Fig. 2B) and glycolipids (data not shown). A 5-mg amount of a neutral fraction from human brain lipids was applied to TC-CCC by using hexane/ethyl acetate/ethanol/0.1% aqueous ammonia (5 5 5 4). Phosphatidylcholine (PC), sphingomyelin (SPM), and lysophosphatidylcholine (lysoPC) were successively eluted. Phosphatidylethanolamine (PE) and lyso-phosphatidylethanolamine (lysoPE) and other minor phospholipid components were retained as the column contents with this solvent system. Cerebroside (fr. 28/36) and some... 

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