Mechanisms tentative

It has been tentatively suggested that one mechanism underlies the Willgerodt reaction and the Kindler modification of it. A labile intermediate is first formed which has a carbon—carbon bond in the side chain. The scheme is indicated below it postulates a series of steps involving the addition of ammonia or amine (R = H or alkyl), elimination of water, re addition and eUmination of ammonia or amine until the unsaturation appears at the end of the chain then an irreversible oxidation between sulphur and the nitrogen compound may occur to produce a thioamide. 

The mechanism of chemiluminescence is still being studied and most mechanistic interpretations should be regarded as tentative. Nevertheless, most chemiluminescent reactions can be classified into (/) peroxide decomposition, including biolurninescence and peroxyoxalate chemiluminescence (2) singlet oxygen chemiluminescence and (J) ion radical or electron-transfer chemiluminescence, which includes electrochemiluminescence. 

In 1973 two papers appeared almost simultaneously (73T101, 73CPB2026) describing the formation, as a minor product, of 3,4,5-trimethoxycarbonyl-l-phenylpyrazole (346) in the reaction between benzaldehyde phenylhydrazone and DMAD (EC=CE). To account for the formation of (346) George et al. (73T101) proposed a tentative mechanism (Scheme 29) involving a Diels-Alder reaction of type (a Figure 25), followed by a retro-Diels-Alder elimination of methyl phenylpropiolate (347). 

Preliminary Selections Assembling background information permits tentative selection of promising equipment and rules out clearly unsuitable types. If the material to be processed is a shiny or pumpable suspension of sohds in a hquid, several methods of mechanical separation may be suitable, and these are classified into setfiiug and filtration... 

At this point in the investigation, the relationship between the pits and the arrowhead-shaped regions of corrosion was uncertain. Several possible causes for the pitting were considered, such as siphonic gas exsolution, biological and/or microbiological activity, and debris (concrete chips, etc.) lodged in the tubes, but each was tentatively dismissed as improbable since none of the proposed mechanisms adequately accounted for all observations. 

Interest in the mechanism and product distribution of thermal and photochemical transformations of aryl azides led to the isolation of some nitrogen-containing derivatives of heptafulvalene. Based on elemental analysis and spectroscopic data it has been suggested tentatively that the compound isolated following vapor-phase pyrolysis of azidopentafluoro-... 

API Specification for Mechanical-Drive Steam Turbines for General Refinery Services (Tentative Standard 615), latest edition. American Petroleum Institute, Division of Refining, Washington, DC. 

Scheme 10.5 Tentative mechanism for cytochrome P450-cata-lyzed epoxidation of a double bond. The reactive iron-oxo species VII (see Scheme 10.4) reacts with the olefin to give a charge transfer (CT) complex. This complex then resolves into the epoxide either through a radical or through a cationic intermediate.

There is a difference in the behavior of benzenediolatoborate and naphthalenedio-latoborate solutions on the one hand, and lithium bis[2,2 -biphenyldiolato(2-)-0,0 ] borate (point 5 in fig. 8) lithium bis[ sali-cylato (2-) Jborate (point 6) or benzene-diolatoborate/phenolate mixed solutions on the other (Fig.8). This can be tentatively explained by the assumption of different decomposition mechanisms due to different structures, which entail the formation of soluble colored quinones from benzenediolatoborate anions and lithium-ion conducting films from solutions of the latter compounds (points 5 and 6) [80], The assumption of a different mechanism and the formation of a lithium-ion conducting, electronically insulating film is supported by... 

There have been few satisfactory demonstrations that decompositions of hydrides, carbides and nitrides proceed by interface reactions, i.e. either nucleation and growth or contracting volume mechanisms. Kinetic studies have not usually been supplemented by microscopic observations and this approach is not easily applied to carbides, where the product is not volatile. The existence of a sigmoid a—time relation is not, by itself, a proof of the occurrence of a nucleation and growth process since an initial slow, or very slow, process may represent the generation of an active surface, e.g. poison removal, or the production of an equilibrium concentration of adsorbed intermediate. The reactions included below are, therefore, tentative classifications based on kinetic indications of interface-type processes, though in most instances this mechanistic interpretation would benefit from more direct experimental support. 

Based on detailed kinetic investigations, a tentative mechanism for this asymmetric oxidation was proposed (Scheme 2) according to which optically active sulphoxides may be formed by two pathways external attack on the sulphur atom by the chiral titanium hydroperoxide (path A) or coordination of sulphur to titanium prior to the oxidation step (path B). Although paths A and B could not be distinguished experimentally, the temperature effect was tentatively ascribed to a change of the mechanism, path A being predominant above — 20 °C and path B becoming competitive at lower temperatures (or vice versa). 

The ratio of negative ion currents, z3]/z3o, was found to be 0.80 0.05. Although production of 15NO might occur partly by abstraction of the J5N rather than the 14N as shown in Reaction 16, this mechanism appears less probable than that indicated. We tentatively conclude that Reaction 15 predominates. 

The wall superheat that corresponds to bubble formation in liquid flow can be estimated using an approach that is not connected to the mechanism of bubble formation. Such tentative estimation makes it possible to consider only the low level of wall superheat. According to Kays and Krawford (1993) the temperature distribution in turbulent flow and Pr 1 is... 

Fig. 11 A tentative mechanism for the reagent-free decarboxylation of ring-fused 2-pyridones obtained under MAOS conditions...

It was shown in the same article that the decarboxylation could also be performed by conventional heating but then copper cyanide was required and a mixture of saturated and imsaturated 2-pyridones 65 and 66 was obtained in a ratio of 1 10 (Fig. 10). A tentative mechanism was suggested for the reagent-free MAOS method where the carbonyl in the 2-pyridone ring is supposed to assist in the decarboxylation yielding an yUde 67 (Fig. 11). The decarboxylated bicyclic 2-pyridone 68 is thereafter obtained after protonation by the solvent. In agreement with the mechanistic suggestion, it was shown that a selective deuteration occurred when deuterated dimethyl sulfoxide (DMSO-de) was used as solvent. 

Fig. 3 Tentative mechanism for the formation of substituted 2-pyridones in the reaction between enaminones and methylene-activated nitriles...

Fig. 5 Tentative mechanism for the formation of 3-substituted 4-hydroxyquinolones 13 in the reaction between anilines and substituted malonic esters via an a-oxoketene 12...

A cyclic mechanism has been tentatively proposed for the reaction involving trialkyltin halides. 

Although superficially this reaction resembles 10-94 it is likely that the mechanism is quite different, involving migration of an R group from boron to carbon (see also 18-23-18-26). The mechanism is not known with certainty, it may be tentatively shown as (illustrated for an a-halo ketone) ... 

Althou sufficient data to provide thorough tests of mechanism are lacking, it is possible to make some tentative conclusions. Sets 15-67, 15-69, and 15-71 give highly significant correlations with eq. (30). These sets include both monosubstituted and disubstituted dienophiles. Obviously, then, both mono-substituted and disubstituted dienophiles lie on the same correlation line and have the same values of a and 3. It therefore seems likely that these sets undergo a concerted mechanism. 

Conclusion The problem areas are tentatively identified the formulations department is asked to improve the flow properties of the granulate and thus decrease the weight dispersion. The maintenance department will now have to find a proposal for countering the excessive wear on one stamp. Note On more modem, heavily instmmented and feed-back controlled tablet presses, the described deviations would have become more readily apparent, and mechanical damage could have been avoided. 

Approaches are required for the following stages identification of toxic species, screening techniques for detecting toxicity, techniques for purifying toxins and provisionally identifying chemical nature, and techniques for tentatively identifying mechanisms of action. 

Techniques for Tentatively Identifying Mechanisms of Action. Once the mechanism by which a toxin kills has been assessed, and toxin reasonably purified, it becomes relevant to try and ascertain as efficiently as possible the cellular mechanisms "tar-getted" by the toxin. This is a necessary step before final analysis of action using pure toxin and site-specific procedures such as the patch-clamp technique. 

Based on the above results and previous works [3,9] on the reaction of epoxides and CO2, we tentatively propose the plausible mechanism for the copolymerization of GMA and CO2 (schane 1), Alkyhnethyl imidazolim salt (QX) and epoxide (GMA) r cted to synthesize an active spedes followed by chain propagation involving a < ncerted insertion of th e epoxide. However, more detailed mechanistic studies are needed to clairly understand the polymerization steps. 

Based on the experimental results above and together with Wang s previous work a tentative mechanism was proposed (Scheme 20) [33]. Thus, intermediate A is formed initially through coordination of imine and alkyne to the Lewis acid. This coordination sets the stage for an addition of the alkyne to the imine leading to the propargylamine intermediate B, which then undergoes an intramolecular... 

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