Group VI

Kinetic evidence indicates that CO dissociation is the first step in the substitution reaction (15), while CO exchange studies suggest cis-CO labilization. The reac- 

Sulphur.- As in previous years a large component of the sulphur chemistry reported has involved the reactions of sulphur-stabilized carbanions, an area that has been covered in Section 1. There has, however, been a good deal of activity in the synthesis and reactions of organosulphur compounds. 

Two interesting fragmentations of a-trimethylsilylsulphides have been used to generate thiocarbonyl ylide (208) and thioaldehydes 

A number of rearrangements involving sulphur have been reported. 

Asymmetric synthesis based on chiral sulphoxides is a rapidly developing field. Two syntheses of (-)-raethyl jasmonate have been accomplished starting from the chiral alkenyl sulphoxide (216 Ar a 

In view of their importance in asymmetric synthesis new routes have been developed to chiral sulphoxides and related species. Sulphinates, useful as precursors of chiral sulphoxides, have been prepared in 40-70% enantiomeric excess and the synthesis and dieno-philic properties of the isomeric sulphinyl acrylates (2l8) and (219) (Ar = 4-MeCgH ) have been described. ( )-Vinyl sulphoxides have been prepared in high optical purity via 1-alkynyl 

The elements in this group have six electrons in their outer quantum level, and can thus achieve a noble gas configuration by acquiring two electrons. 

Some of the more important physical properties of the elements are given in Table 10.1. 

All the elements are able to share two electrons forming two covalent bonds. The two covalent bonds formed by oxygen can be separate bonds, for example 

Elmenl /((MIC mker Outer elecimtis 4(oiiiir rahi (nni) Rdus ofX (nm) m.p. (K) 6.p. (K) Ele 4 (kJn x-.r Iron tiilf of ) x-.x=- k iom sHlIon kJmol ) Electro- ite0eilv (Pauling) 

The covalently bonded oxygen atom still has two lone pairs of electrons and can act as an electron pair donor. It rarely donates both pairs (to achieve 4-coordination) and usually only one donor bond is formed. A water molecule, for example, can donate to a proton, forming H30, and diethyl ether can donate to an acceptor such as boron trifluoride  

Element Atomic timber Outer electrons. 4lomirs radius M Mas ofX2 (nm) m.p. IK) b.p. IK) Ele 4 (kJ i x-r Iron nity wr1) X- X 1st ionisation energy, IkJmor1) Electro- negativity (Pauling) 

Sulphur. In acyclic compounds containing sulphur-sulphur bonds inversion at the sulphur is relatively easy, but in the cyclic compound (62) there is no evidence for inversion at sulphur. The first n.m.r. kinetic study of ring inversion for a 1,4-dithian has been of the perfluoro-compound 

Inversion in the cyclic sulphite (65) and the cyclic sulphate (66) has been studied by ultrasonic techniques. Isomerisation of the cyclic iron-sulphur derivative (67) appears, from kinetic evidence, to take place by an intramolecular inversion process.  

Solvent exchange is merely a special case of substitution. However, this topic will be treated separately, as a more convenient arrangement of material can be thus achieved. Solvent exchange involving unmixed solvates in pure solvents will be discussed first, followed by mixed ligand complexes in pure solvents, then solvent exchange in mixed solvents. Proton exchange between bulk and co-ordinated solvents is covered in the final section. 

The formation and stability constants of complexes between Pd (Pt. Rh, Ir, Os, Ru) and o-coumaric acid have been determined by pH titration.31 The results indicate that a 1 2 complex is formed with Pd. 

A study of the olefin oxidation catalyst system, palladium acetate-MOAc (M = Li or Na), has shown that in the absence of acetate ion, Pd acetate-acetic acid exists as the trimeric species [Pd3(OAc)6].32 Reaction with MOAc is not instantaneous, and u.v.-visible spectra indicate an initial equilibrium involving trimer - dimer (9). When M = Na conversion into dimer is complete at 0.2M-NaOAc. Further addition of 

Baba and S. Kawaguchi, lnorg. Nuclear Chem. Letters, 1973, 9, 1287. 

This complex has two free chelate centres and reacts with [Rh(acac)(CO)2] in C6H6 at 70°C to yield the novel trinuclear complex [Pd Sal=N—N=SalRh(CO)2 2]. The synthesis of the ternary oxide K2Pd02 has been effected by reaction between K20 and PdO.34 X-Ray studies (Table 1, p. 400). suggest a chain structure which corresponds to that of K2PdS2. 

Oxygen.—A kinetic study of the decomposition of triethyloxonium salts, [OEtalA ([A] =[BF4] , [PFe] , or [SbFg]-) in methylene chloride has been studied. The decomposition is strongly affected by the presence of EtOEt or dioxan. The mechanism is suggested to involve a four-centre transition state.  

Sulphur.—Ab initio calculations indicate that a weak [RsSg] complex is an intermediate in the exchange reaction between R SSR and [R S] . The calculations indicate a linear species, with the charge located on the peripheral sulphur 

Rate-determining reactions between [NaSgOe] and [OH], and [SgOe] and [H+] are suggested. There is a report of the kinetics of formation and decomposition of the higher polythionic acids. The acid-catalysed hydrolysis of methyl toluene-p-sulphenate, ArS(OMe), has been studied in moist organic solvents  

H2O + ArSS(Ar)S(OAr)— -ArSSAr + ArSOaH ArSOaH + ArSOMe— ArSSOaAr -I- MeOH ArSS(Ar)S(OAr) -1- MeOH-- -ArSSAr + ArS(0)0Me 

The same workers have also studied the racemization of (+)-methyl / -tolyI sulphoxide in acetic acid and in nitrobenzene reaction is catalysed by the chloride ion, and a chlorsulphonium ion is suggested as an intermediate. The racemization can occur by the reaction 

With an excess of cyanide an additional, slower process (21) is observed. For 

X = S it is found that AH = 6.3kcalmol and AS = — 40cal mol for X = Se the reaction is very much faster, and activation parameters were not measured. CyanidesubstitutionsinPhSOg(X) S02Ph(X = SorSe, = lor2)and in [OaSSeSOal - have also been reported. Other studies on related systems have appeared. The reduction of A -tosylsulphilimines, R R SNTs, with cyanide ion to 

Cermak and M. Smutek, Coll. Czech. Chem. Comm., 1975,40,3241,3265 V. N. Plakhotnik and A. Kh. Drabkina, Vopr. Khimii i Khim. Tekhnol. Resp. Mezhved. Temat. Nauch—Tekhn. Sbornik, 1975, 37, 51 Chem. Abs., 1976, 84, 50333). 

The decomposition of a range of substituted benzenesulphonyl chlorides in 1 % aqueous dioxan have been examined kinetically, and there have been further studies of the cleavage of arylalkylsulphonates by electron donors. The decomposition of trifluoromethanesulphonic acid in aqueous solution at high temperatures (571—593 K) has been examined. Two pathways, reactions (22) and (23), can be 

The intermediate undergoes a further reaction (24). This can occur by nucleophilic 3PhS-SOPh + 2[OH]------------------ -2Ph-S-S-Ph + 2[PhS02]- + H2O (24) 

It should be noted that this is a true pre- quUibriuin since third-order kinetics are maintained even at high [MeCN]. Steady-state treatment of [(16)] leads to 

Photolysis of a variety of [W(CO) (a-diimine)] ccmplexes in the presence of PR3 ( R = alkyl, Ph, or MeO) effects substitution of a carbonyl ligand. Quantum yields are low and depend on the basicity, cone angle and concentration of the PR- indicating an 

W chelate = substituted bipy or phen, 2,2 -bi(4H-5,6-dihydro-thiazine) biacetylbis (phenylimine) or 4,4 -bipyrimidine ].  

In the course of these studies some bis-chelating ligands have been used to generate complexes of type (9) as well as analogous 

The relative sizes of 12 PR ligands have been assessed by determining the cis trans ratios of [W(CO) (PR )L] complexes obtained from reactions of [W(CO) (py)L], [L = PPhMe / PPh2Et, or P(tol- )2] with PR. Generally, decreasing cis trans ratios 

Other complexes containing unidentate ligands that have been 

Oxygen.—A kinetic study of the reaction DjOs - DaO + Oa, in DaO solution, has revealed the rate law for this process. The activation energy is 17.5 kcal mol-i in O.OlM-DClOi.  

Oxygen.— The rates of hydrolysis of oxygen difluoride in basic aqueous solution show a one-third-order dependence on hydroxide-ion concentration. At pH = 10, the activation energy for this hydrolysis is 8.5kcalmol. The rate law for photolysis of hydrogen peroxide, in the presence of hydroxyl-amine or of methylamine, is 

Quantum yields, which were pH dependent, were lower in the presence of the named additives. A chain mechanism for these photolyses is presented and discussed. 

Activation parameters for the alkaline hydrolysis of pyrosulphate (SaO ) have been recorded as Ea = 11.0 0.12kcal mol and A5 = 39.05 0.41 cal deg mol. Initial rates of reaction of thiosulphate with hydrochloric acid, in aqueous solution, indicate the rate law 

The rate-determining step is therefore thought to be reaction between SaO and its conjugate acid HS2O3 the eventual product is colloidal sulphur. At an ionic strength of 0.035 mol 1 , the activation energy is 15.93 0.1e kcal mol and the frequency factor 1.64( 0.13) x 10. The rate of subsequent formation of elemental sulphur is a function of the surface area of that sulphur which has already precipitated. In acid solution dithionates decompose thus  

The dependence of the rate of this reaction on the acidity function /r in sulphuric acid of concentration 7—10 mol 1 suggests that the transition state is derived from monoprotonated dithionate. The Arrhenius plot for this reaction is curved a surprisingly high activation enthalpy of 52kcalmoI (25 °C) is reported. The rate law for the reaction of peroxomonosulphate with hydroxide is 

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The usual acceptor and donor dopants for Al Ga As compounds are elements from groups II, IV and VI of the periodic table. Group II elements are acceptors and group VI elements are donors. Depending on the growth conditions. Si and Ge can be either donors or acceptor, i.e. amphoteric. This is of special interest in LEDs. 

These apparent anomalies are readily explained. Elements in Group V. for example, have five electrons in their outer quantum level, but with the one exception of nitrogen, they all have unfilled (I orbitals. Thus, with the exception of nitrogen. Group V elements are able to use all their five outer electrons to form five covalent bonds. Similarly elements in Group VI, with the exception of oxygen, are able to form six covalent bonds for example in SF. The outer quantum level, however, is still incomplete, a situation found for all covalent compounds formed by elements after Period 2. and all have the ability to accept electron pairs from other molecules although the stability of the compounds formed may be low. This... 

For the most part it is true to say that the chemistry of the alkali and alkaline earth metal compounds is not that of the metal ion but rather that of the anion with which the ion is associated. Where appropriate, therefore, the chemistry of these compounds will be discussed in other sections, for example nitrates with Group V compounds, sulphates with Group VI compounds, and only a few compounds will be discussed here. 

All Group VI elements form a hydride HjX. With the notable exception of water, they are all poisonous gases with very unpleasant smells. Table 10.2 gives some of their important physical properties. 

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