Parallel format

They varied only the values of the adsorption and desorption rate constants of the reaction intermediate B, and by using the simplest Langmuir kinetics, they calculated time-concentration curves of compounds A, B, and C shown in Fig. 5. Also from this example, which does not consider any step as clearly rate determining, it is evident how very different concentration versus time plots can be obtained for the same sequence of surface reactions if adsorption and desorption of the intermediate B proceed by different rates, which are, however, comparable with the rate of surface reactions. In particular, the curves in the first and second columns of Fig. 5 simulate the parallel formation of substances B and C, at least... 

Purely parallel reactions are e.g. competitive reactions which are frequently carried out purposefully, with the aim of estimating relative reactivities of reactants these will be discussed elsewhere (Section IV.E). Several kinetic studies have been made of noncompetitive parallel reactions. The examples may be parallel formation of benzene and methylcyclo-pentane by simultaneous dehydrogenation and isomerization of cyclohexane on rhenium-paladium or on platinum catalysts on suitable supports (88, 89), parallel formation of mesityl oxide, acetone, and phorone from diacetone alcohol on an acidic ion exchanger (41), disproportionation of amines on alumina, accompanied by olefin-forming elimination (20), dehydrogenation of butane coupled with hydrogenation of ethylene or propylene on a chromia-alumina catalyst (24), or parallel formation of ethyl-, methylethyl-, and vinylethylbenzene from diethylbenzene on faujasite (89a). 

DNA microarrays, or DNA chips consist of thousands of individual DNA sequences arrayed at a high density on a single matrix, usually glass slides or quartz wafers, but sometimes on nylon substrates. Probes with known identity are used to determine complementary binding, thus allowing the analysis of gene expression, DNA sequence variation or protein levels in a highly parallel format. 

Quite complex kinetic behavior has been identified on some surfaces. For instance, on Ir(100), the TPD data from NO-saturated surfaces display two N2 desorption peaks, one at 346 K from the decomposition of bridge-bonded NO, and a second at 475 K from the decomposition of atop-bonded NO molecules [13], Interestingly, the first feature is quite narrow, indicating an autocatalytic process for which the parallel formation of N20 appears to be the crucial step. An additional complication arises from the fact that this Ir(100) surface undergoes a (1x5) reconstruction, and that NO adsorbed on the metastable unreconstructed (lxl) phase leads to N2 desorption at lower temperatures. In another example, on the reconstructed hexagonal Pt(100) surface, when a mixed NO + CO adsorbed layer is heated, a so-called surface explosion is observed where the reaction products (N2, C02 and N20) desorb simultaneously in the form of sharp peaks with half-widths of only 7 to 20 K. The shape of the TPD spectra suggests again an autocatalytic mechanism [14],... 

The disulfonamide library was tested in the TifO PrC-mcdiatcd addition of Et2Zn to aldehydes, a known process using the bis-trifluoromethylsulfonamide of 1,2-diaminocyclohexane.106 The tests were run in 30 different reaction vessels in parallel format. In order to increase throughput, each vessel was charged with four different aldehydes, and the enantioselectivities of the four reaction products were determined by conventional GC analysis of the crude mixtures. The idea of using a given catalyst to screen combinatorially the reactions of different substrates had previously been proposed but in a different context.45 In the present case each mixture required about one hour to be screened, which means that about 96 ee-determinations of products (52) (Scheme 11) could be performed per day.105 A total of 120 results were collected, the best ees being >90%. 

A different multicomponent route to imidazoles has been described by the group of O Shea, involving the diversity-tolerant three-component condensation of an aldehyde, a 2-oxo-thioacetamide, and an alkyl bromide (5 equivalents) in the presence of ammonium acetate (Scheme 6.201) [364]. This allowed the preparation of a 24-membered 4(5)-alkylthio-lH-imidazole demonstration library from 21 different aldehydes, 12 alkyl bromides, and two 2-oxo-thioacetamides. The library was synthesized in a parallel format using a custom-built reaction vessel. Alkylthioimidazoles... 

Antisite defects in the pyrochore structure Er2Ti207 were mentioned previously (Section 1.10). These defects also occur in the nonstoichiometric compound Er2.09Ti194O6.952, which is slightly Er203-rich compared to the stoichiometric parent phase. The formation of the antisite pair is now accompanied by the parallel formation of oxygen vacancies ... 

The preparation of individual compounds in a parallel format such that the structural identity of each is known by its physical location in a matrix... 

The kinetics of the parallel formation of by-products is generally similar to the kinetics of the main reaction (i.e. rate independent of the oxygen pressure and first order with respect to propene), which presumes identical reaction steps. A study of the origin of acetaldehyde and formaldehyde carried out by Gorshkov et al. [144] is of interest in this connection. 14C-Labelled propene was oxidized over a bismuth molybdate catalyst at 460° C the results showed that acrolein, acetaldehyde and formaldehyde are formed via a symmetrical intermediate, presumably one and the same intermediate. The study, moreover, shows that acetaldehyde is exclusively formed from this intermediate, while formaldehyde may also be formed from the aldehyde group of acrolein and the methyl group of acetaldehyde. 

Alternative structures arise that provide parallel formation pathways and consequently slow nucleation kinetics. 

A 20-membered library of 1,3,5-lriazincs was prepared in a parallel format employing a one-pot, three-component condensation of anilines, dicyandi-amide and acetone. The reaction time was reduced from 22 hours (reflux in... 

The first block DIV is a frequency divider. This block has 2 modes of operation, the normal mode and the test mode. In the test mode, the UART chip runs 16 times faster than in the normal mode. Also, the transmission data rate of the UART chip is 16 times faster than the receiving rate. Each block is initialized by setting the reset line low by applying a 0 to port MR. The TX block accepts 8-bit parallel data from the microprocessor interface (MP) block and transmits it serially to the RS-232 port through port DOUT. Conversely, the RX block receives serial data input, and sends it in 8-bit parallel format to the MP block. Again, the transmitter runs at 16 times the speed of the receiver. The microprocessor interface (MP) block asynchronously controls the parallel data flow between the RX / TX blocks and the microprocessor data bus. 

It was of interest in this respect to determine which rhodium carbonyl complexes result from the former reaction and whether the parallel formation of any organic products derived from the hydrogenation of carbon monoxide Is also occurring. The latter possibility was considered because of the presence of hydrides In the cluster and the involvement of hydrido carbonyl complexes in the hydrogenation of carbon monoxide. Unfortunately, It was not possible to detect any organic products formed from this reaction even after the cyclic repetition of the transformations below (equation 14). 

This alkoxy derivative of copper is obviously not stable in the presence of too much water its presence under catalytic conditions has been confirmed by the parallel formation of some alkoxycarbonate probably through the known reaction ... 

In conclusion, the parallel formation of succinates is in agreement with tlie C9dstence of the o organometallic species proposed as an intermediate in the acrylate synthesis. 

ADH catalyzes the oxidation process in the cytosol of the hepatocyte, forming a complex of ethanol, ADH and NAD". The reaction consists in transferring the hydrogen from the ethanol molecule to NAD" with parallel formation of acetaldehyde. 

Upon contacting 1.3 Torr propene enzene (1/6) mixture with HP at 453 K, fast formation of cumene and the disappearance of the OH bands (the active centres of reaction) were observed. After the first 20 minutes the development of cumene bands stopped, while the parallel formation of alkenyl carbenium ions increased slightly and continuously with reaction time. 

HCR involving complex polyatomic molecules usually occur via a large number of steps and result in the parallel formation of several products. In this case, the reaction rate and selectivity may easily be affected by the geometric details of nm-sized catalyst particles. To simulate such reactions, one can use (with proper modifications) general approaches developed [58] to describe adsorption of complex... 

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