Other Synthesis Routes

The synthesis routes described in the previous section are certainly not the only potential strategies towards the development of degradable polyesters. In the upcoming paragraphs, some alternative research efforts will be described which were beyond the focus of the previous sections. 

In addition to the polymerisation of pure lactones, these cyclic [di] esters have already been included as co-monomer to improve the properties of closely related polymers like polyamide obtained starting from lactams [86]. 

Sanhao et al. have proposed to utilise a Baylis-Hillman type reaction between dialdehydes and diacrylates to obtain polymers with a polyester backbone and alcohol and double bond side-groups [87]. The authors reported this material to be a very interesting intermediate towards side-chain modified polymers. 

As the field progresses, an increasing amount of research is performed on novel polyester architectures and properties. These include among others block copolymers [88, 89], dendrimers [90, 

cyclic poly(esters] [92], star-shaped polymers [58, 59, 93], responsive materials [94, 95], stereocontrolled polymerisations [96], etc. 

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Other Synthesis Routes. Several alternative routes to the nucleopbilic substitution synthesis of polysulfones are possible. Polyethersulfone can be synthesized by the electrophilic Eriedel-Crafts reaction of bis(4-chlorosulfonylphen5l)ether [121 -63-1] with diphenyl ether [101-84-8] (11—13). 

Calcination. Only low concentrations of the surfactants are required such that the concentrations are well below the critical micelle concentration (rather than 25% in mass usually observed in other synthesis routes). Hence calcination may well be a viable process for the large scale preparation of these materials. Sample controlled Thermal Analysis has been used to study the highly controlled pyrolysis of the mesophase including the mechanism of the extraction of the template. 

Other synthesis methods have also been developed but may not be practiced on a large commercial scale as compared to those indicated above. Examples of syntheses that begin from liquid phase precursors include the sol-gel, hydrothermal, and Pechini methods. In the course of these reaction schemes, polycondensation or precipitation occurs, and the volatile components are removed, often by thermal methods. Other synthesis routes to ceramic materials include the nitridation of metals to form metal nitrides and the carbothermal reduction of oxides to form carbides and borides. 

The LSCEs represent a new class of macromolecular systems distinguished by macroscopically uniform anisotropy. The concept of LSCE can be furthermore extended to other synthesis routes and to the densely crosslinked systems. Macroscopic uniaxially oriented films can be formed by mechanical force, alignment surface [30], magnetic and electric fields [31], polarized light [32], etc., and then crosslinked to form an anisotropic network (LC network is abbreviated as LCN) if the mixture components contain polymerizable or crosslink-able bifunctional monomers (Figure 9.13). Alternatively, amorphous or liquid crystalline side-group and/or main-chain polymers incorporating additional... 

SevCTal types of reactions may be employed in hydrothermal synthesis (69). A common feature is that precipitation of the product generally involves forced hydrolysis undCT elevated temperature and pressure. TTie powders have several desirable characteristics, but they also suffer from a few disadvantages so that their benefits are normally not fully realized. In hydrothermal synthesis, the crystalline phase is commonly produced directly so that a calcination step is not required, as in the case of several other synthesis routes. The powders also have the characteristics of very fine size (10-100 nm), narrow size distribution, singlecrystal particles, high purity, and good chemical homogeneity. 

More details and other synthesis routes are given in Ref. [160]. 

Also, nitrobenzene is used to produce 4-aminodiphenylamine to produce 6PPD anti-ozonant more efficiently than other synthesis routes. 

This way, metal hydroxide fluorides are accessible in which the metal site is coordinated by both anions, hydroxide and fluoride, thus presenting real hydroxide fluorides that are almost inaccessible via any other synthesis route [58], By varying the F to OH ratio, the whole series of M(OH)jF , from M(OH) to MF can be synthesized. As a result, the Lewis to Brpnsted acid site ratio of these materials can be tuned over a wide range resulting in optimized solid catalysts with high potential for a wide range of acid-base-catalyzed reactions [40,52],... 

Just as a researcher will perform a literature synthesis for a compound, there are computer programs for determining a synthesis route. These programs have a number of names, among them synthesis design systems (SDS) or computer-aided organic synthesis (CAOS) or several other names. 

The program is used by first building the target molecule. It then generates a list of possible precursors. The user can choose which precursor to use and then obtain a list of precursors to it. The reaction name and conditions can also be displayed. Once a satisfactory synthesis route is found, it can be printed without all the other possible precursors included. The drawing mode worked well and the documentation was well written. 

Other possible chemical synthesis routes for lactic acid include base-cataly2ed degradation of sugars oxidation of propylene glycol reaction of acetaldehyde, carbon monoxide, and water at elevated temperatures and pressures hydrolysis of chloropropionic acid (prepared by chlorination of propionic acid) nitric acid oxidation of propylene etc. None of these routes has led to a technically and economically viable process (6). 

The single-monomer route (eq. 5) is preferred as it proves to give more linear and para-linked repeat unit stmctures than the two-monomer route. Other sulfone-based polymers can be similarly produced from sulfonyl haUdes with aromatic hydrocarbons. The key step in these polymerisations is the formation of the carbon—sulfur bond. High polymers are achievable via this synthesis route although the resulting polymers are not always completely linear. 

Pyrrohdinone (2-pyrrohdone, butyrolactam or 2-Pyrol) (27) was first reported in 1889 as a product of the dehydration of 4-aminobutanoic acid (49). The synthesis used for commercial manufacture, ie, condensation of butyrolactone with ammonia at high temperatures, was first described in 1936 (50). Other synthetic routes include carbon monoxide insertion into allylamine (51,52), hydrolytic hydrogenation of succinonitnle (53,54), and hydrogenation of ammoniacal solutions of maleic or succinic acids (55—57). Properties of 2-pyrrohdinone are Hsted in Table 2. 2-Pyrrohdinone is completely miscible with water, lower alcohols, lower ketones, ether, ethyl acetate, chloroform, and benzene. It is soluble to ca 1 wt % in aUphatic hydrocarbons. 

Other synthetic routes to pyrazinones and quinoxalinones are from the halo compounds, by dealkylation of ethers (8lJCS(Pl)3111> or by diazotization of the corresponding amines, but since the halo derivatives are normally derived from the hydroxy compounds, and the amines from the halo derivatives, direct synthesis seems to represent the most practical approach. 

Rogers and Hallam (1991) provide other examples of chemical approaches to inherent safety, involving synthesis routes, reagents, catalysts and solvents. 

Examples of Synthesis Routes Inherently Safer Than Others As summarized by Bodor (1995), the ethyl ester of DDT is highly effective as a pesticide and is not as toxic. The ester is hydrolytically sensitive and metabolizes to nontoxic products. The deliberate introduction of a structure into the molecule which facilitates hydrolytic deactivation of the molecule to a safer form can be a key to creating a chemical product with the desired pesticide effects but without the undesired environmental effects. This technique is being used extensively in the pharmaceutical industry. It is applicable to other chemical industries as well. 

Photochemical Wolff rearrangement of 2-diazo-3-ketones, though not widely used as a source of A-norsteroids, is discussed in section V in connection with the mechanism of the important photochemical synthesis of D-norsteroids. Photochemical rearrangement of epoxy ketones is a source of A-nosteroids these rearrangements are discussed in chapter 13. Other photochemical routes to A-norsteroids are known." " ... 

Butadiene can be alternatively produced by other synthetic routes discussed with the synthesis of isoprene, the second major diolefin for rubber production. 

Several routes to such derivatives have been covered already by primary synthesis (Chapter 1), from quinoxalinecarboxylic acids (Section 7.1.2), from quinoxalinecarboxylic esters (Section 7.2.2), and from quinoxalinecarbonyl halides (Section 7.3). Other preparative routes are illustrated in the following classified examples. 

No synthesis of (3) appears in the original paper so we may speculate on the success of these or other ideas. Route (a) is much shorter as no carboxyl protection is necessary if we are ready to waste the first mole of ylid. 

In the near future, the possible synthesis of nanotubes with solid-gas potential will be more favorable to adsorption. The effect of hydrogen overpressure on the stability of adsorbed Ha needs to be verified in the near future. The high-purity nanotube produced by laser vaporization, catalytic decomposition, or other techniques should be investigated. It is noteworthy that the synthesis of the SWNT with defined diameters and distances between the walls is difficult to perform at present, but future synthesis routes will allow more... 

The relative contribution of any flow in this life cycle to the total global-warming score of the production of a unit mass of product 6 is shown. The highest shares in the impact score are exhibited by the two substrates, because their production is taken into account, comprising multi-step synthesis routes starting from crude oil. All other input mass flows show relatively small contributions (maximum of 4% for solvent 2). This is due to relatively high... 

The route also provides a satisfactory path to some alkyl silicates for which no other satisfactory routes are available. Some of these alkyl silicates may be of interest in the synthesis of ceramics by the sol-gel technique. 

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