Sodium species

In many syntheses activation is not effected by sonochemical preparation of the metal alone but rather by sonication of a mixture of the metal and an organic reagent(s). The first example was published many years ago by Renaud, who reported the beneficial role of sonication in the preparation of organo-lithium, magnesium, and mercury compounds [86]. For many years, these important findings were not followed up but nowadays this approach is very common in sonochemistry. In another early example an ultrasonic probe (25 kHz) was used to accelerate the preparation of radical anions [87]. Unusually for this synthesis of benzoquinoline sodium species (5) the metal was used in the form of a cube attached to the horn and preparation times in diethyl ether were reduced from 48 h (reflux using sodium wire) to 45 min using ultrasound. 

The reaction mechanism is similar to that of alkylbenzenes, but the conditions differ somewhat. Promoters are often not necessary because sodium adds across the azometine linkage of pyridines to yield ionic sodium species (49, 50). A soluble-catalyst system is formed in contrast to the nonsoluble system in aromatic hydrocarbons. Temperatures of 125-160° are sufficient for both ethylation and propylation of most compounds. 

Lime Reactor The efflnent from the EDV system is pumped to an agitated reactor vessel where the EDV efflnent is reacted with lime to form calcium sulfite and active sodium species via the following reactions ... 

With reference to sodium species and to Figure 1, the ion exchange reaction... 

Considering an example of leaching under moderate pH excursion, such that the autoprotolysis of water can be neglected and k+ and k are approximately constant, the balance of sodium species in the system obeys the following set of equations (4)... 

For the hydrated Y zeolites, sample spinning rates of 3 to 5 KHz were used in most cases. A typical spectrum was acquired using 1000 scans, a recycle time of 0.5 sec. and an rf excitation pulse width of 2.0 microsec, which is less than 1/4 of a 90° pulse width of sodium in solution. Under these conditions, the integrated intensity of the different sodium NMR lines in the spectrum closely approximates the concentration of different sodium species giving rise to the NMR lines. For the dehydrated Y zeolites, samples, spinning rates of 6 to 9 KHz were used. A typical spectrum was acquired using 5000 scans, a 2 sec. recycle time and a pulse width less than that of a solids 45° pulse (about 2.5 microsec). 

One result of Frankland s research was the realization that alkyl groups could be transferred intact from one atom to another. If the recipient atom were a metal, another organometallic formed if the recipient were carbon or a nonmetal, a purely organic compound was the result. In 1855, Wiirtz (293) demonstrated this by reacting alkyl iodides with sodium metal to produce hydrocarbons. Frankland and his students performed a variety of syntheses using organozinc or organo-sodium species (96, 100, 101), Eq, (4) is typical of this work ... 

The endo-endo conformation of cryptands can be internally protonated to form proton cryptates. With the small cryptands, e.g. [1.1.1]- and [2.1.1]-cryptand (15a and 15b), the two internal protons are so efficiently shielded from H2O and OH that deprotonation only very slowly occurs even in strong base (8UA6044). Alkali cation cryptates are able to stabilize unusual species as their counterions. Dye and coworkers have isolated several alkali metal anions by this method. The sodium species (Na [2.2.2]cryptand Na ) was obtained as gold metallic crystals and gave a Na NMR with a broad Na -cryptate resonance and a narrow, upheld Na resonance. The other alkali metals show similar behavior and an electride salt (Na [2.2.2]cryptand e l has even been isolated (B-79MI52105). Crystalline anionic clusters of the heavy post-transition metals (such as Sb7 , Pbs , Sng ) were first obtained with alkali metal cryptates as the counterions (75JA6267). 

B Na REDOR NMR has been used to probe the spatial relationship between the network former (boron) and the network modifier (sodium) species in sodium borate glasses. Under conditions of fast MAS, site resolved REDOR data have been obtained, revealing that the trigonal and tetrahedral units interact more or less equally strongly with the sodium ions. 

The metal also plays a role. The presence of a highly covalent 0—Li bond favors the trans product, but a more ionic O—Na or O—K bond, in alcoholic solvents, favors the cis.- " The lithium species is less bulky, due to poorer solvation in the aprotic solvent. The protic solvent hydrogen bonds extensively with the ionic sodium species, leading to a large increase in the relative size of the alkoxide moiety. This bulky group influences the geometry of the intermediate and leads to an increase in the cis product.- ... 

Figure 3.7 Which of these sodium species do students consider stable ...

Carbanionic species in solution are strongly influenced by the counterion and by any added species such as bases that can coordinate a metallic counterion. For example, Kronzer and Sandel reported NMR studies of 1-and 2-naphthylmethyllithium, -sodium, and -potassium in tetrahydrofuran (THF) and in hexamethylphosphoramide (HMPA) solution. In THF the spectra showed a strong dependence on the metal, suggesting that there was close association of the carbanionic carbon with the metal. The spectra of the lithium and sodium species were identical in HMPA solution, however, suggesting that the carbanions were significantly separated from the cation, either as free ions or as ion pairs separated by solvent molecules. 

Most thermal sources used in atomic spectrometry provide temperatures in the range 1500-7000°C. Even at extreme temperamres, a majority of the neutral atoms exist in the ground state. Table 1 provides some indication of the temperature-dependent population of the first excited state for Na, which is relatively easily populated. The table also shows the population of the first excited state of Zn, whose transition energy, in contrast, is more than twice that of Na. At the higher temperatures, ionization can become appreciable and a majority of the analyte may exist as the ionized species, although, those sodium species still present as neutral atoms will still exhibit the relative populations shown in Table 1. 

When the sodium atom in sodium aluminum hydride is replaced with a lithium atom, it is found that lithium aluminum hydride readily dehydrogenates, with faster kinetics and at lower temperatures than the sodium species [48, 49]. One might conclude that the decompositimi is related to the aluminum component of the anion, especially because structural analysis of the decompositions shows that there is a stable intermediate of AlHs in both the lithium and sodium cases. The faster kinetics and lower decomposition temperature are also expected, as lithium hydride is substantially more stable that sodium hydride, with stability measured by the heat of formation of each molecule [50]. 

The data utilised for the thermodynamic properties of sodium species are listed in Table 6.6. 

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