Calcium, Strontium and Barium

Formation of organocalcium reagents from chiral 1-halocyclopropanes with ArH, Ca (e.g. ArH= biphenyl or naphthalene) has been shown to proceed via a S.E.T. mechanism, which provides free radicals in solution as intermediates. Addition of 6,6-Me2-fu vene to a suspension of M(Ca or Sr), activated by HgCl2, in THF produces air-sensitive (4 M=Ca L =nothing M=Sr, L =(THF)2]. 

Calcium containing about 0.5% magnesium and only traces (0.002%) of sodium reacts smoothly at — 70°C with organic iodides in THF to give reasonable yields of RCal (R = Me, 93% Et, 68% Pr, 57% Ph (at -30T), 97%). Aryl derivatives have also been obtained in diethyl ether. Addition of dioxan precipitates colourless ArCal. dioxan, from which dioxan can be removed in vacuo at 110°C giving base-free ArCal. 

In general reactivity, organocalcium compounds behave more like organolith-ium derivatives than like Grignard reagents. Thus Bu CaI resembles Bu Li in forming Bu CO as well as Bu CO H (after hydrolysis) on reaction with carbon dioxide. Alkylcalcium halides also bring about the polymerization of butadiene or of styrene by an anionic mechanism. 

Several dialkyls and diaryls of calcium have been prepared from the corresponding mercury derivatives R2Hg and calcium or calcium amalgam in THF. Again experimental technique is crucial to success the quality of the metal, its state of division and the cleanliness of its surface are especially important. Nevertheless, dimethylcalcium has been obtained in 96% yield as a white solid sparingly soluble in THF. Dialkyls and diaryls of Sr and Ba are even more difficult to prepare. Diethylstrontium attacks THF above — 30°C. The reaction between Et Hg and Sr was initiated at - 10°C for 15 minutes and then completed during 

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The alkali metals of Group I are found chiefly as the chlorides (in the earth s crust and in sea water), and also as sulphates and carbonates. Lithium occurs as the aluminatesilicate minerals, spodimene and lepidolite. Of the Group II metals (beryllium to barium) beryllium, the rarest, occurs as the aluminatesilicate, beryl-magnesium is found as the carbonate and (with calcium) as the double carbonate dolomite-, calcium, strontium and barium all occur as carbonates, calcium carbonate being very plentiful as limestone. 

Calcium, strontium and barium produce characteristic flame colours like the Group 1 cations (calcium, orange strontium, red barium, green) and flame photometry can be used for their estimation. All give insoluble carbonates in neutral solution. 

At room temperature, sulfur unites readily with copper, silver, and mercury and vigorously with sodium, potassium, calcium, strontium, and barium to form sulfides. Iron, chromium, tungsten, nickel, and cobalt react much less readily. In a finely divided state, zinc, tin, iron, and aluminum react with sulfur on heating (19). 

Resoles are usually those phenolics made under alkaline conditions with an excess of aldehyde. The name denotes a phenol alcohol, which is the dominant species in most resoles. The most common catalyst is sodium hydroxide, though lithium, potassium, magnesium, calcium, strontium, and barium hydroxides or oxides are also frequently used. Amine catalysis is also common. Occasionally, a Lewis acid salt, such as zinc acetate or tin chloride will be used to achieve some special property. Due to inclusion of excess aldehyde, resoles are capable of curing without addition of methylene donors. Although cure accelerators are available, it is common to cure resoles by application of heat alone. 

In 1817 Dobereiner found that if certain elements were combined with oxygen in binary compounds, a numerical relationship could be discerned among the equivalent weights of these compounds. Thus when oxides of calcium, strontium, and barium were considered, the equivalent weight of strontium oxide was approximately the mean of those of calcium oxide and barium oxide. The three elements in question, strontium, calcium, and barium were said to form a triad. 

W. E. Lindsell in Structure oj Magnesium, Calcium, Strontium, and Barium Compounds in Comprehensive Organometallic Chemistry, G. Wilkinson. F. G. A. Stone, E. W. Abel. Eds., Vol. 1. pp 155-252. Pergamon, Oxford 1982. 

A.B. Tsent-Kurnakova R.P. Vasd eva, Synthesis of Calcium, Strontium, and Barium Peroxide Compounds in Hydrogen Peroxide Vapours , IzvAkadNaukSSSR,SerKhim (12), 2738-40 (1967) CA 68, 110875 (1968)... 

Calcium, strontium, and barium are called the alkaline earth metals, because their earths —the old name for oxides—are basic (alkaline). The name alkaline earth metals is often extended to all the members of Group 2 (Table 14.4). 

The true alkaline earth metals—calcium, strontium, and barium—are obtained either by electrolysis or by reduction with aluminum in a version of the thermite process (see Fig. 6.8) ... 

Goldschmidt predicted from his empirical rule that calcium chloride would not have the fluorite structure, and he states that on investigation he has actually found it not to crystallize in the cubic system. Our theoretical deduction of the transition radius ratio allows us to predict that of the halides of magnesium, calcium, strontium and barium only calcium fluoride, strontium fluoride and chloride, and barium fluoride, chloride,... 

Lead peroxide is even more active than the oxide. It reacts violently with sulphur and sulphides. When it is ground up with sulphur, the mixture combusts. With hydrogen sulphide, the reaction is very exothermic and causes peroxide to incandesce and hydrogen sulphide to combust. Finally, it reacts violently with calcium, strontium and barium sulphides on heating. 

Calcium, strontium and barium azides are not shock-sensitive, but explode on heating at about 150, 170 and 225 (or 152)°C, respectively. In sealed tubes, the explosion temperatures are higher [1], Although calcium azide is rather mildly endothermic (AH°f (s) +46 kJ/mol, 0.37 kJ/g), it can decompose much more exothermally to the nitride (189.9 kJ/mol, 1.53 kJ/g) than to the elements [2],... 

Although the first report of an organometallic compound of the heavier alkaline earth metals appeared near the beginning of the twentieth century,291 the RMX Grignard analogs of Ca, Sr, and Ba never fulfilled their promise as general-purpose synthetic reagents. More difficult to form, less thermally stable, and less selective in their reactions than their Mg counterparts, the literature data of the compounds was often contradictory, and many syntheses were irreproducible (see Calcium, Strontium, and Barium in COMC (1982)). 

The use of sterically bulky ligands to provide kinetic stability to compounds of the heavier group 2 elements has become widely practiced, and has facilitated the synthesis of diorganyl complexes of various types. Advances in the organometallic chemistry of bonded compounds of calcium, strontium, and barium have been reviewed. 

Table 5 Metallocenes of calcium, strontium, and barium and their Lewis base adducts...

It is also possible to isolate bis(carbene) complexes involving the heavier alkaline earth metals. Thus, the reaction of two equivalents of 4 (R = Me or (Bu, R = H) with calcium, strontium and barium bis(trimethylsilyl)amides [M N(SiMe3)2 2(thf)2] (M = Ca, Sr, Ba) resulted in the displacement of two thf molecules to afford the corresponding biscarbene species, 19 (19). The solubilities and stabilities of these complexes were found to decrease from calcium to barium. 

Marinho EP, Souza AG, de Melo DS, Santos IMG, Melo DMA, and da Silva WJ. Lanthanum chromites partially substituted by calcium strontium and barium synthesized by urea combustion—Thermogravimetric study. J. Thermal Analysis Calorimetry 2007 87 801-804. 

Suarze DL. Beryllium, magnesium, calcium, strontium, and barium. In Bartels JM (ed.), Methods of Soil Analysis Part 3 Chemical Methods. Madison, WI Soil Science Society of America and American Society of Agronomy 1996, pp. 575-601. 

Most hydroxides (OH ) are insoluble except those of Group IA metals, calcium, strontium, and barium. (Later we will see that these are strong bases.)... 

Alkali metal (Group IA) hydroxides (LiOH, NaOH, KOH, RbOH and CsOH) Calcium, strontium, and barium hydroxides... 

Another salt-like group of compounds that have acid-base properties is the hydrides of the alkali metals and calcium, strontium, and barium. These hydrides will react with water to form the hydroxide ion and hydrogen gas ... 

Flame photometry is the name given to the technique that measures the intensity of the light emitted by analyte atoms in a flame. It is the oldest of all the atomic techniques. It is not highly applicable because of the low temperature of the flame. Only a handful of elements can be measured with this technique, including sodium, potassium, lithium, calcium, strontium, and barium. The technique was formerly used... 

The metalation of trialkylsilylphosphane and -arsane with the alkaline earth metal bis[bis(trimethylsilyl)amides] of calcium, strontium, and barium yields the mixed phosphanides and phosphanediides as well as arsanides and arsanediides depending on the stoichiometry and the demand of the trialkylsily] substituents according to Scheme 3.6-11. The main feature is the M2E3 bipyramid with the metal atoms in apical positions. These cages are often interconnected via common faces (61, 63, 64, 65, 67, and 69). A substitution of the phosphanide substituents by other Lewis bases such as THF or benzonitrile is not possible for these compounds and, consequently, homoleptic phosphanediides and arsanediides with inner M4E4 heterocubane moieties are so far unknown for M = Ca, Sr, and Ba. In all these cases a further metalation to obtain homoleptic phosphanediides failed. 

Homoleptic alkaline earth metal phosphanediides and arsanediides of calcium, strontium, and barium are unknown thus far, a consequence of the use of rather mild metalating reagents, because dialkylcalcium, -strontium, and -barium are at present not easily accessible [73]. 

Calcium, strontium and barium are strongly chemically reactive. For safety reasons and for protection from contamination their handling must be carried out under dry inert conditions wearing goggles, shields, etc. 

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