Subsequent steps

The subsequent steps do not in principle differ from those of the Coarse analysis, see Section 22.2. In JSA, there are requirements to comprehensiveness and no hazards are too insignificant to be documented. All hazards will sooner or later result in injuries or near accidents, if they are not remedied. 

In estimating the risk of accidents, working time has to be considered. Usually, the job is carried out by one or a few operators, and Table 22.5 is in this case most suitable. It represents the acceptance criteria for the total risk of an individual operator working about 2000 hours a year. The contribution from the analysed job has to be evaluated in relation to the total risk to which the operator is exposed. 

Exercise Establish a job-safety analysis team. Select a hazardous job that at least one of the team members is familiar with. Assign different roles in the group and perform a job-safety analysis. Document the results in a record sheet according to Table 23.1. 

---

Homogeneous catalysts. With a homogeneous catalyst, the reaction proceeds entirely in the vapor or liquid phase. The catalyst may modify the reaction mechanism by participation in the reaction but is regenerated in a subsequent step. The catalyst is then free to promote further reaction. An example of such a homogeneous catalytic reaction is the production of acetic anhydride. In the first stage of the process, acetic acid is pyrolyzed to ketene in the gas phase at TOO C ... 

The first task was the aeation of large 3D chemical structure databases. By devising so-called fast Automatic 3D model builder, software such as the CORINA [27, 28] and CONCORD [29, 30] programs resulted in a boom in 3D database development (see Section 2.9 in this book and Chapter II, Section 7.1 in the Handbook). A subsequent step was the development of fast... 

Pimelic acid. This may be prepared from 1 5-peiitanediol or tetra-hydropyran, through the dibromide (Sections 111,35 and 111,37) and dinitrile exactly as described for Suberic Acid. An alternative method for the preparation of 1 5-dibromopentane, together with full details of the subsequent steps, is given in the following Section. 

Each transform should lead to reagents, which are more easily accessible than the target molecule. In the subsequent steps of antithesis the reagents are defined as new target molecules, and the transform procedure is repeated until the reagents needed are identical with commercially available starting materials. 

Cation (Section 1 2) Positively charged ion Cellobiose (Section 25 14) A disacchande in which two glu cose units are joined by a 3(1 4) linkage Cellobiose is oh tamed by the hydrolysis of cellulose Cellulose (Section 25 15) A polysaccharide in which thou sands of glucose units are joined by 3(1 4) linkages Center of symmetry (Section 7 3) A point in the center of a structure located so that a line drawn from it to any element of the structure when extended an equal distance in the op posite direction encounters an identical element Benzene for example has a center of symmetry Cham reaction (Section 4 17) Reaction mechanism m which a sequence of individual steps repeats itself many times usu ally because a reactive intermediate consumed m one step is regenerated m a subsequent step The halogenation of alkanes is a chain reaction proceeding via free radical intermediates... 

The acceleration is determined and the cycle renewed. In the subsequent steps, the velocities advance from t-1/2 At to t-tl/2 At. The resulting set of positions and velocities is the molecular dynamics trajectory. 

Decomposition (fragmentation) of a proportion of the molecular ions (M +) to form fragment ions (A B+, etc.) occurs mostly in the ion source, and the assembly of ions (M +, A+, etc.) is injected into the mass analyzer. For chemical ionization (Cl), the Initial ionization step is the same as in El, but the subsequent steps are different (Figure 1.1). For Cl, the gas pressure in the ion source is typically increased to 10 mbar (and sometimes even up to atmospheric pressure) by injecting a reagent gas (R in Figure 1.1). 

The subsequent step is to identify the various scenarios which could cause loss of control of the hazard and result in an accident. This is perhaps the most difficult step in the procedure. Many accidents have been the result of improper characterization of the accident scenarios. For a reasonably complex chemical process, there might exist dozens, or even hundreds, of scenarios for each hazard. The essential part of the analysis is to select the scenarios which are deemed credible and worst case. 

The methodology used in the preparation of RU 486 (84) and other ll -steroids is shown. Conjugate addition of a cuprate reagent to the a,P-unsaturated epoxide (85) provides the liP-substituted steroid (86) stereospecificaHy (131). Subsequent steps lead to the synthesis of RU 486 (84). 

Excess alkylating reagent is required if the tetraorganotin is desired as the exclusive product. In commercial practice, the stoichiometry is kept at or below 4 1, since the cmde product is usually redistributed to lower organotin chlorides in a subsequent step and an ether is used as the solvent (86). The use of diethyl ether in the Grignard reaction has been generally replaced with tetrahydrofuran. 

Work in the mid-1970s demonstrated that the vitamin K-dependent step in prothrombin synthesis was the conversion of glutamyl residues to y-carboxyglutamyl residues. Subsequent studies more cleady defined the role of vitamin K in this conversion and have led to the current theory that the vitamin K-dependent carboxylation reaction is essentially a two-step process which first involves generation of a carbanion at the y-position of the glutamyl (Gla) residue. This event is coupled with the epoxidation of the reduced form of vitamin K and in a subsequent step, the carbanion is carboxylated (77—80). Studies have provided thermochemical confirmation for the mechanism of vitamin K and have shown the oxidation of vitamin KH2 (15) can produce a base of sufficient strength to deprotonate the y-position of the glutamate (81—83). 

The purification of saccharified starch depends on the raw material used, and may be different from plant to plant. When the starch slurry is hquefied ia a jet cooker the saccharification process is carried out at 55—65°C, pH 4—4.5, for 24—72 hours. The subsequent steps consist of filtration or centrifiigation, ion exchange, isomerization, treatment with activated carbon, and evaporation to form a storage-stable product. 

In organisms which produce cephalosporin and cephamycins, the configuration of the O -aminoadipyl side chain of (30) is D, while penicillin producers yield the l isomer. The exact point at which the configuration is inverted is unknown. Subsequent steps in cephalosporin biosynthesis are believed to involve ring expansion to deacetoxycephalosporin C (31), which may proceed by a mechanism analogous to the chemical pathway (see Section 5.10.4.2), followed by hydroxylation and acetylation at C-3 to produce cephalosporin C (32). 

Membrane Processes Membrane processes are also used diafiltration is convenient for the removal of small contaminating species such as salts and smaller proteins, and can be combined with subsequent steps to concentrate the protein. Provided that proper membrane materials have been selected to avoid protein-membrane interactions, diafiltration using ultrafiltration membranes is typically straightforward, high-yielding and capital-sparing. These operations can often tolerate the concentration or the desired protein to its solu-bihty limit, maximizing process efficiency. 

Measurement versus Equipment Performance Pumps that are in reasonable condition typically operate within 5 percent of their pump curve. Consequently, pressures and flows that are inconsistent with the pump curve imply that the indicated flow and/or pressure are incorrecl . Figure 30-16 shows a single impeller curve plotted as head versus flow. The point shown is inconsistent with the pump operation. Therefore, that pair of flow and pressure measurements is not validated and should not be used in the subsequent steps. 

Inadequate removal of solvent leading to unwanted reaction in downstream equipment or in subsequent steps. 

If the pressure coefficient is now, or was in an earlier step, 5% uiutei the 0.29 value, calculate a new mean blade velocity using the rounded off number of stages and the original pressure coefficient, 0.29. Use the calculated blade velocity in the subsequent step for compressor speed Calculate the speed. 

Such diagrams make clear the difference between an intermediate and a transition state. An intermediate lies in a depression on the potential energy curve. Thus, it will have a finite lifetime. The actual lifetime will depend on the depth of the depression. A shallow depression implies a low activation energy for the subsequent step, and therefore a short lifetime. The deeper the depression, the longer is the lifetime of the intermediate. The situation at a transition state is quite different. It has only fleeting existence and represents an energy maximum on the reaction path. 

The double bond transposition could also be achieved by the conversion of an intermediate for PGA2 synthesis into a 1,3-diene iron tricarbonyl complex from which PGC2 was synthesized in four steps. The Fe(CO)3 diene complex which survived the Wittig reaction was cleanly removed by Collins reagent in the subsequent step (Ref. 10). 

Chain reaction (Section 4.17) Reaction mechanism in which a sequence of individual steps repeats itself many times, usually because a reactive intermediate consumed in one step is regenerated in a subsequent step. The halogenation of alkanes is a chain reaction proceeding via free-radical intermediates. 

Al. A fast preequilibrium protonation of substrate followed by a slow ratedetermining reaction of the protonated substrate. Subsequent steps (such as attack by water) are fast. 

This optimization was very close to a minimum at step two, but then it moved away from it again in subsequent steps. Merely increasing the number of steps will not fix the problem. A better approach is to start a new optimization, beginning with the structure corresponding to step 2 and including the CalcFC option in the route section. 

MP4/6-311G(d,p) at the optimized geometry from step 2. Vario corrections will be made to this energy in subsequent steps. Note that u energy is obtained from the job run for Step 6. 

Pyruvate produced by glycolysis is a significant source of acetyl-CoA for the TCA cycle. Because, in eukaryotic ceils, glycolysis occurs in the cytoplasm, whereas the TCA cycle reactions and ail subsequent steps of aerobic metabolism take place in the mitochondria, pyruvate must first enter the mitochondria to enter the TCA cycle. The oxidative decarboxylation of pyruvate to acetyl-CoA,... 

A cyanide anion as a nucleophile adds to an aldehyde molecule 1, leading to the anionic species 3. The acidity of the aldehydic proton is increased by the adjacent cyano group therefore the tautomeric carbanion species 4 can be formed and then add to another aldehyde molecule. In subsequent steps the product molecule becomes stabilized through loss of the cyanide ion, thus yielding the benzoin 2 ... 

Mechanistically this reaction is described as a concerted pericyclic [3,3] sigma-tropic rearrangement. A carbon-oxygen bond is cleaved and a carbon-carbon bond is formed. In a subsequent step the initial product 4 tautomerizes to the stable aromatic allylphenol 3 ... 

---