Preparative method

Gel chromatography on a preparative scale is a very complex and expensive experiment. However, it attracts some interest as a means of producing calibration standards for analytical GPC and recent papers have described fraction- 

Analytical Gel Pomeation Chromatt raphy.—Since its discovery in 1964, analytical GPC has rapidly become the single most important technique for characterization of the size of polymer molecules. The basic experiment has changed very little, the major development being the adaptation of high speed chromatographic methods to GPC giving much shorter analysis times. The literature up to 1976 has been extensively reviewed.  

Podesva, Angew. Makromol. Chem., 1978, 72, 185. 

Although GPC calibration is well studied and many satisfactory methods exist, this is less true for chromatogram broadening corrections. In principle, the observed chromatogram F V) for a polymer is related to the true chromatogram in the absence of broadening fV(Y) by Tung s equation  

Copolymers present a double problem in GPC it is difficult to define an appropriate calibration method and compositional heterogeneity can alter detector responses. For these reasons quantitative studies of copolymers are rare although Janca et al. have published an extensive study of the behaviour of vinyl acetate-vinyl chloride copolymers. Elgert and Wohlschiess have used a combination of refractive index and ultraviolet detection to study compositional heterogeneity in copolymers of a-methyl styrene with butadiene. Studies of ethylene-propylene copolymers have been reported by Osawa and Inaba.  

Lanthanide alkoxide complexes can be prepared using a number of methods. The key difference lies in the nature of lanthanide starting materials. These include elemental metals, halides, alkoxides, amides, carboxylates, hydrides, and organometallic species [1, 11], The organic ligands come from aliphatic alcohols, phenols, or their metal salts. 

This method makes use of the production of a less soluble metal salt (MX) to drive the reaction to completion. One commonly encountered problem with this route is the low solubility of the starting lanthanide halides. Exposure to anhydrous NH3 gas helps dissolve lanthanide halides [22]. Eollowing the addition of alkali metal and the appropriate alcohols, the desired alkoxide complexes can be obtained. This reaction is thought to proceed with the formation of a triamide 

This silylamide route has attracted enormous attention as pure alkoxide complexes may be obtained directly [23]. The success of this reaction hinges upon the volatility of the amine byproduct that drives the reaction to completion [24]. Apotential concern is that the amide starting complexes are prepared by the reaction of lanthanide halides with alkali metal amides. High-purity, halide-free amides are thus critical to the success of this synthetic method. 

In this chapter, we highlight the preparative methods, which have been used successfully to produce active, selective and durable nanogold catalysts and look at their properties and the reactions which they promote. We then consider the potential commercial applications for these new catalysts and look into the future. 

For gold to be an active catalyst, use of a careful preparation procedure is crucial in order to obtain it as nanoparticles well dispersed on the oxide support. In this section we describe the methods devised for the preparation of these nanoparticulate gold catalysts. Catalysts are thought to be most active in the 2- to 5-nm gold particle range but both smaller and larger particles have also been shown to have activity and may play a significant role. 

In this section, the corrinoids, the other macrocyclic complexes, and the cyanides are dealt with separately (Sections A-C). The preparative organo-metallic chemist will be primarily interested in Sections B and C, whereas 

The experimental details are mentioned as they arise often air must be excluded from the reactions but there are many examples when this exclusion is not important (or may even be fatal ) to the reaction. A general point is that nearly all of these organocobalt(III) complexes are unstable to visible light, and so light should be excluded during the preparations at all times whenever the organocobalt(III) complex is in solution. The solid complexes are stable to visible light. 

Details of complexes which have been prepared are given in Table III, 1-29. 

The Preparation and Characterization of Organocobalt(III) Complexes of the General Formula [RCo (L )X] where L4 is the equatorial ligand (Corrin, etc.) and X is the unidentate axial ligand (.S,6-dimethylbenzimidazole, HjO or absent, where L is corrin otherwise as stated in the table). 

The following classification and abbreviations are used in the Table. Methods of preparation (for details see Sections III and IV) 

Mylius (M60) described the preparation of many calcium aluminate hydrates and related compounds. As with C-S-H, it is normally essential to exclude atmospheric CO2 and to avoid prolonged contact with glass apparatus. Dosch and Keller (D20) described methods for obtaining many AFm phases by anion exchange or other special procedures. 

The C4A and CjA hydrates are most conveniently prepared by adding CaO or saturated CH solution to a supersaturated calcium aluminate solution obtained by shaking CA or white calcium aluminate cement (Section 10.1.1) with water. Such solutions typically contain up to about 1.2gCa01 and 1.9 g AljOj 1 , these concentrations depending on the shaking time, temperature, proportioning and particle size of the starting 

Monosulphate is troublesome to prepare. Mylius mixed 500 ml of a supersaturated calcium aluminate solution (649 mg CaO and 969 mg Al203l ) at 18°C, with shaking, with 2924ml of saturated CH (1.25gCa01 ) and 334ml of saturated gypsum (1.93gCaS041 ). After 30 min, crystallization was complete the mixture was filtered, washed four times with a little water followed by 96% ethanol and ether, and dried over CaClj and soda lime without evacuation. Monosulphate may also be prepared hydrothermally (A8). 

Crammond (C32) reviewed reports of the formation of thaumasite in the laboratory and in deteriorated building materials. It forms readily at 4 C from mixtures that contain the appropriate ions and also 0.4-1.0% of reactive alumina. It does not form at 25°C or above. A little AP may be essential, and reported failures to reproduce published syntheses may be due to the use of aluminium-free materials. 

Generally, terminal-hydride complexes are prepared from metal halides, their phosphine derivatives, or organometallic complexes either by the action of a hydridometallate or dihydrogen in THF, alcohols, or other solvents. Potassium, sodium, sodium amalgam, and magnesium are also used as reducing agents. Some examples of preparative reactions are shown below 

Hydrolysis of complex salts and oxidative addition (p. 27) of weak acids are also utilized frequently  

Electrochemical polymerisation produces films on an electrode surface.. Under controlled conditions uniform films up to a few mm thick, which carl be removed from the electrode for subsequent study, can be prepared. Physical properties can be modified by choice of the counterions (dopants) included in the film during growth. It is, however, more difficult to control chain structure and crosslinking than in chemical methods. Electrochemically produced polymers are, therefore, less well characterised than the best directly-synthesised polymers. While this is less satisfactory for fundamental investigations, it is of less concern for applications such as battery electrodes, artificial muscles and drug release agents. The two main approaches, direct-synthesis and electrochemical, are described in the following two sections. 

The next major improvement in sample quality was the result of developments in direct synthesis. Oriented samples were obtained by the polymerisation of acetylene with the conventional titanium catalyst on a single crystal substrate and in nematic liquid crystals, see Tsukamoto (1992). Heat-treating the catalyst was found to produce polymer that could be stretched to give oriented samples. This resulted in a higher electrical conductivity along the orientation direction, up to 2xl05 fl-lm-1 being obtained. Naarman and co-workers heat treated the catalyst at 393 K and carried out the reaction in silicone oil at room temperature (Theophilou et al., 1986). Silicone oil was chosen as it has the same viscosity at room temperature as the usual solvents 

ROMP has also been used to obtain soluble PAc by polymerisation of cyc/o-octatetraenes mono-substituted with aryl or alkyl units (Gorman et al., 1993). The product is a PAc with one substituent every four repeat units, sufficient to impart solubility without adverse consequences for backbone conjugation. 

There have been major improvements in the quality of PAc samples and consequent enhancement of physical properties. Nevertheless, the instability of PAc under a normal atmosphere prompted the focus of synthetic work to switch to other, more stable, polymers as the emphasis changed from fundamental studies to application at the turn of the century. 

The introduction of bridging groups on the thiophene ring modifies the physical and chemical properties of the polymers obtained. The energy of the optical absorption is reduced in FEDOT, Fig. 9.2(k), and poly(ijothia-naphthalene), (PITN) (Wudl et al., 1984), so that in the conductive state thin films are transparent. PEDOT shows high electrochemical stability in the oxidised state and, when combined with poly(styrenesulphonic acid) counter ions, can be processed from aqueous solution. 

There is not sufficient space to discuss all vinylidene complexes which have been reported, for example over 200 crystal structures are listed in the CCDC. Consequently, this article largely concentrates on the chemistry of metal vinylidene complexes which has been described since 1995. Vinylidene complexes are generally available for the metals of Groups 4—9, with several reactions of Group 10 alkynyls being supposed to proceed via intermediate vinylidenes. However, few of the latter compounds have yet been isolated. This chapter contains a summary of various preparative methods available, followed by a survey of stoichiometric reactions of vinylidene-metal complexes. A short section covers several non-catalytic reactions which are considered to proceed via vinylidene complexes. The latter, however, have been neither isolated nor detected under the prevailing conditions. 

The main synthetic approaches to metal-vinylidene complexes will be discussed under the following headings  

Synthesis of 2-heterocyclic thiosemicarbazones can be summarized in three reaction sequences following the lead of Klayman et al. [5]. Condensation of equimolar quantities of a thiosemicarbazide and a 2-heterocyclic aldehyde or ketone in an alcoholic solvent is represented by Eq. (1). The product s superscripts refer to positions of substitution in the thiosemicarbazone moiety in accord with lUPAC. 

The most common method of preparing thiosemicarbazones with substituents other than hydrogen attached to N involves amination of the appropriate 

S-methyldithiocarbazate. The reaction sequence (2) starts with the ketone and hydrazine carbodithioate. A third synthetic method, Eq. (3), which has proven most useful for attaching a heterocyclic ring at on the thiosemiearbazone moiety [111], is shown below  

Synthesis of 2-heterocyclic thiosemicarbazones can also be accomplished by transamination with acetonitrile the most commonly used solvent [112], N-dialkyl- or JV-arylalkyl-functions are the best leaving groups. For example, 2-acetylpyridine N-dimethylthiosemicarbazone prepared by Eq. (2) can be used as a starting material to prepare other 2-actylpyridine thiosemicarbazones. 

In the preparation of solids, care usually has to be taken to use stoichiometric quantities, pure starting materials, and to ensure that the reaction has gone to completion because it is usually not possible to purify a solid once it has formed. 

We do not have space here to discuss all the ingenious syntheses that have been employed over the past few years, so we shall concentrate on those that are commonly used with a few examples of techniques used for solids with particularly interesting properties. The preparation of organic solid state compounds and polymers is not covered because, generally, it involves organic synthesis techniques which is a whole field in itself, and is covered in many organic textbooks. 

FIGURE 3.1 The basic apparatus for the ceramic method (a) pestles and mortars for fine grinding (b) a 

Solid state reactions up to 2300 K are usually carried out in furnaces which use resistance heating the resistance of a metal element results in electrical energy being 

Containers must be used for the reactions which can both withstand high temperatures and are also sufficiently inert not to react themselves suitable crucibles are commonly 

For purposes of comparison it should be noted that very powerful metallating agents (e.g., butyllithium/TMEDA or butyllithium/potassium t-butoxide) are capable of abstracting two or even three protons from various alkylated dienes. Thus, various hexadienes and methyl pentadienes have been converted to dianionic species, while 2,4-dimethyl-l,4-pentadiene, 1,4-heptadiene, and 1,4-cycloheptadiene have all been converted to trianions84-86.  

Yost and Margerison treated the halocyanoamide 6 with three equivalents of lithium aluminum hydride and obtained 1,5-diazocine 7 (R = H, 

R1 = Me) (64FRP1378964 66USP3247206). Gatta and Landi-Vittory reacted N-phenyl- and Af-benzyl,)V-(3-chlorophenyl)anthranilamides with potassium carbonate and isolated 1,5-benzodiazocinones 8 (70FES830). The bisamide 9 was reductively cyclized using diborane to afford the dia-zocine 10 (70USP3488345). 

Singh and Mehta heated an enamine postulated as either structure 19 or 20 with concentrated sulfuric acid and obtained the cyclopentenodia-zocinethione 21 (77IJC(B)786). Topliss and co-workers reductively cy- 

Interesting heterocycle-fused 1,5-benzodiazocines have been prepared. Two different groups have synthesized triazolo-l,5-benzodiazocines 24 by cyclization of triazolobenzophenones 25 (74JAP74/85095 80JMC392), while pyrazolo-l,5-benzodiazocines 26 (R = Me, Ph) have been isolated by cyclization of 27 (R = Me, R = NH2) and by reductive cyclization of 27 (R = Ph, R1 = N02) (79JHC935). 

Cyclization of Amino Carboxylic Acids and Related Compounds 

It would therefore seem logical to directly control the potential of the working electrode, and it is likely that well-known electrolytic preparations in organic chemistry could be improved with respect to product purity by a more systematic application of controlled-potential electrolysis. However, potentiostatic reductions can be slow, and this is one reason for the preferred use of a large current, even if controlled, in many electro-organic syntheses. 

Controlled-potential electrolysis yields a product which may be identified in situ, e.g., spectrometrically, or after isolation from the solution. In the former case, both stable and unstable products may be studied, whereas isolation is usually limited to stable compounds. The methods used for identification of the product will also depend upon the stability of that product. Electron spin resonance, ultraviolet spectrophotometry, and cyclic voltammetry have proved useful techniques for the identification of unstable (radical) species. The presence of water in the electrolyzed solution usually prevents the use of in situ infrared (but not Raman) spectrophotometric analysis, and the use of such powerful techniques as nuclear magnetic resonance and mass spectrometry is also excluded unless the product can be isolated in a reasonably pure state. 

Electrolysis may be carried out continuously, i.e., the selected potential is applied to the working electrode for the duration of the reaction, or an intermittent procedure may be used in which the potential is periodically changed or interrupted so that electrolysis ceases. The use of a dropping 

The use of preparative methods in studies of organic electrochemical reactions has been reviewed and examples of the identification of both unstable and stable intermediates and products have been presented. This review includes some interesting observations upon the fact, referred to above, that different products may be obtained from a given reaction if it is carried out at a mercury pool rather that a dropping mercury electrode. 

It is difficult to present reaction techniques in an order which is obviously logical and sequential. In the following pages the pattern usually adopted is to move from the simple to the complicated, although simplicity has its own complications. So, the first reaction considered is a simple gas-phase reaction between molecules, but one for which a quite complicated glass vacuum line would be needed. The reaction between aqueous Cu and aqueous ammonia, considered later, can be carried out using a couple of test tubes, but is chemically quite complex. 

The properties of a polymer nanocomposites and their improvement with respect to the traditional composites depend on the structure and morphology developed during the preparation step. In turn, structure and morphology depend on preparation conditions. 

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The exact methods employed to prepare any particular surface for study vary from material to material, and are usually detennined empirically. In some respects, sample preparation is more of an art than a science. Thus, it is always best to consult the literature to look for preparation methods before starting with a new material. 

Laser photolysis of a precursor may also be used to generate a reagent. In a crossed-beam study of the D + FI2 reaction [24], a hypertliennal beam of deuterium atoms (0.5 to 1 eV translational energy) was prepared by 248 mn photolysis of DI. This preparation method has been widely used for the preparation of molecular free radicals, both in beams and in experiments in a cell, with laser detection of the products. Laser photolysis as a method to prepare reagents in experiments in which the products are optically detected is fiirtlier discussed below. 

For some volatile aliphatic 1,2,3-trienes simple preparative methods have been b4-55... 

The majority of preparative methods which have been used for obtaining cyclopropane derivatives involve carbene addition to an olefmic bond, if acetylenes are used in the reaction, cyclopropenes are obtained. Heteroatom-substituted or vinyl cydopropanes come from alkenyl bromides or enol acetates (A. de Meijere, 1979 E. J. Corey, 1975 B E. Wenkert, 1970 A). The carbenes needed for cyclopropane syntheses can be obtained in situ by a-elimination of hydrogen halides with strong bases (R. Kdstcr, 1971 E.J. Corey, 1975 B), by copper catalyzed decomposition of diazo compounds (E. Wenkert, 1970 A S.D. Burke, 1979 N.J. Turro, 1966), or by reductive elimination of iodine from gem-diiodides (J. Nishimura, 1969 D. Wen-disch, 1971 J.M. Denis, 1972 H.E. Simmons, 1973 C. Girard, 1974),... 

Many examples of insertions of internal alkynes are known. Internal alkynes react with aryl halides in the presence of formate to afford the trisubstituted alkenes[271,272]. In the reaction of the terminal alkyne 388 with two molecules of iodobenzene. the first step is the formation of the phenylacetylene 389. Then the internal alkyne bond, thus produced, inserts into the phenyl-Pd bond to give 390. Finally, hydrogenolysis with formic acid yields the trisubstituted alkene 391(273,274], This sequence of reactions is a good preparative method for trisubstituted alkenes from terminal alkynes. 

Triflates of phenols are carbonylated to form aromatic esters by using PhjP[328]. The reaction is 500 times faster if dppp is used[329]. This reaction is a good preparative method for benzoates from phenols and naphthoates (473) from naphthols. Carbonylation of the bis-triflate of axially chiral 1,1 -binaphthyl-2,2 -diol (474) using dppp was claimed to give the monocarboxy-late 475(330]. However, the optically pure dicarboxylate 476 is obtained under similar conditions[331]. The use of 4.4 equiv. of a hindered amine (ethyldiisopropylamine) is crucial for the dicarbonylation. The use of more or less than 4.4 equiv. of the amine gives the monoester 475. 

The thioboration of terminal alkynes with 9-(alkylthio)-9-borabicyclo[3.3.1]-nonanes (9-RS-9-BBN) proceeds regio- and stereoselectively by catalysis of Pd(Ph,P)4 to produce the 9-[(Z)-2-(alkylthio)-l-alkeny)]-9-BBN derivative 667 in high yields. The protonation of the product 667 with MeOH affords the Markownikov adduct 668 of thiol to 1-alkyne. One-pot synthesis of alkenyl sulfide derivatives 669 via the Pd-catalyzed thioboration-cross-coupling sequence is also possible. Another preparative method for alkenyl sulfides is the Pd-catalyzed cross-coupling of 9-alkyl-9-BBN with l-bromo-l-phe-nylthioethene or 2-bromo-l-phenylthio-l-alkene[534]. 

Aryl halides react with a wide variety of aryl-, alkenyl- and alkylstan-nanes[548-550]. Coupling of an aryl tritlate with an arylstannane is a good preparative method for diaryls such as 688. The coupling of alkenylstannanes with alkenyl halides proceeds stereospecifically to give conjugated dienes 689. The allylstannane 690 is used for allylation[397,546,551-553]. Aryl and enol triflates react with organostannanes smoothly in the presence of LiCl[554]. 

Arenediazonium salts are also used for the couplina[563], (Z)-Stilbene was obtained unexpectedly by the reaction of the ti-stannylstyrene 694 by addition-elimination. This is a good preparative method for cu-stilbene[564]. The rather inactive aryl chloride 695 can be used for coupling with organostannanes by the coordination of Cr(CO)3 on aromatic rings[3.565]. 

Substituted aroyl- and heteroaroyltrimethylsilanes (acylsilanes) are prepared by the coupling of an aroyl chloride with (Me3Si)2 without decarbonylation, and this chemistry is treated in Section 1.2[629], Under certain conditions, aroyl chlorides react with disilanes after decarbonylation. Thus the reaction of aroyl chlorides with disilane via decarbonylation is a good preparative method for aromatic silicon compounds. As an interesting application, trimel-litic anhydride chloride (764) reacts with dichlorotetramethyidisilane to afford 4-chlorodimethylsilylphthalic anhydride (765), which is converted into 766 and used for polymerization[630]. When the reaction is carried out in a non-polar solvent, biphthalic anhydride (767) is formed[631]. Benzylchlorodimethylsilane (768) is obtained by the coupling of benzyl chloride with dichlorotetramethyl-disilane[632,633]. 

The reaction of an azide[185,186] or a trimethylsilylazide(I87] followed by the treatment with Ph3P is another preparative method for the primary allylic amine 307. 

The preparative method for the Pd(0) catalyst active in these regioselective eliminations under mild conditions is crucial. The very active catalyst is prepared by mixing equimolar amounts of Pd(OAc) or Pd(acac)2 and pure n-... 

Another preparative method for the enone 554 is the reaction of the enol acetate 553 with allyl methyl carbonate using a bimetallic catalyst of Pd and Tin methoxide[354,358]. The enone formation is competitive with the allylation reaction (see Section 2.4.1). MeCN as a solvent and a low Pd to ligand ratio favor enone formation. Two regioisomeric steroidal dienones, 558 and 559, are prepared regioselectively from the respective dienol acetates 556 and 557 formed from the steroidal a, /3-unsaturated ketone 555. Enone formation from both silyl enol ethers and enol acetates proceeds via 7r-allylpalladium enolates as common intermediates. 

These compounds may be obtained by the Hantszch heterocyciization method (see Chapter II, Section 11.3). A -widely used two-step preparative method (Scheme 195) involves initial reaction of a 2-amiriothiazole -with 339 in pyridine (631-638) in aqueous sodium carbonate (639) or by fusion without solvent (640). The formed 340 is then hydrolyzed in acidic (641, 642, 1593) or alkaline medium (643-646). The direct reaction of 342 (Scheme 196) -with 2-aminothiazoles is less common and takes place in... 

The first member of the series. 2-imino-3,4-dimethyl-4-thiazoline (363) is obtained when the di-HBr salt of bis(methylformamidine)disulfide (362i is refluxed for 16 hr in acetone (Scheme 209) (700). The most common preparative methods involve direct heterocyclization by the Hantzsch method (see Chapter II. Section II.4), though the mechanism of this reaction suggests certain limitations according to the respective natures of R2, R3, and in 364 (Scheme 210). 

The rearrangement discovered by Kolosova et al. probably involves such reactivit (159). This reaction provides a good preparative method for various 5-amino-methylthiazoles (Scheme 43). No mechanism is proposed in the report, and it is not easy to understand how the C-5 enamine-like position competes with the very nucleophilic thiocarbonyl group of the formed A-4-thiazoline-2-thione. An alternative mechanism could start with ethanol addition at C-2. leading to the A-4-thiazoline (90) (Scheme 44). In this intermediate, C-5 nucleophilic reactivity would be favored bv the true enaminic structure. After alkylation on C-5,... 

Selenium heterocycles receive far less mention in the literature than do such homologs as oxazole, thiazole, or imidazole. In fact, preparative methods of selenium heterocycles are much more limited than for the other series, mainly because of manipulatory difficulties arising from the toxicity of selenium (hydrogen selenide is even more toxic) that can produce severe damage to the skin, lungs, kidneys, and eyes. Another source of difficulty is the reactivity of the heterocycle itself, which can easily undergo fission, depending on the reaction medium and the nature of the substituents. 

Asinger et a], have developed a simple preparative method for variously substituted A3-thiazolines by the action of sulfur and ammonia on ketones. 

Different preparative methods of thiazolecarboxaldehyde have been reported by Iversen and Lund (97) ... 

When a preparative method for an aldonic acid is re quired bromine oxidation is used The aldonic acid is formed as its lactone More properly described as a reaction of the anomeric hy droxyl group than of a free aldehyde... 

Today the most efficient catalysts are complex mixed metal oxides that consist of Bi, Mo, Fe, Ni, and/or Co, K, and either P, B, W, or Sb. Many additional combinations of metals have been patented, along with specific catalyst preparation methods. Most catalysts used commercially today are extmded neat metal oxides as opposed to supported impregnated metal oxides. Propylene conversions are generally better than 93%. Acrolein selectivities of 80 to 90% are typical. 

Powder Preparation. The goal in powder preparation is to achieve a ceramic powder which yields a product satisfying specified performance standards. Examples of the most important powder preparation methods for electronic ceramics include mixing/calcination, coprecipitation from solvents, hydrothermal processing, and metal organic decomposition. The trend in powder synthesis is toward powders having particle sizes less than 1 p.m and Httie or no hard agglomerates for enhanced reactivity and uniformity. Examples of the four basic methods are presented in Table 2 for the preparation of BaTiO powder. Reviews of these synthesis techniques can be found in the Hterature (2,5). 

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