Trace of products

A short-path distillation apparatus is used, the distillate (oxa-spiropentane plus dichloromethane) being trapped in a reeeiver placed in a methanol-dry ice bath cooled to — 80°. The checkers found it useful to drive out last traces of product by adding several milliliters of dichloromethane to the residual thick paste and distilling. The proton magnetic resonance spectrum (dichloromethane) shows an oetet at 8 0.85 and a singlet at S 3.00 in the ratio 4 2. 

To keep product yield at a maximum it is important that the solubility of product in the spent acid be kept to a minimum. This also facilitates removal of traces of product from the spent acid so that it can be either fortified and reused, reused to make lower nitro compds, or neutralized and discharged as non-polluting waste material... 

The last traces of product can be driven into the receiver by warming the stillhead with a heat gun. 

Most measurements of the rates of enzyme-catalyzed reactions employ relatively short time periods, conditions that approximate initial rate conditions. Under these conditions, only traces of product accumulate, hence the rate of the reverse reaction is negligible. The initial velocity (vj) of the reaction thus is essentially that of... 

GPC traces of products of the reductive coupling of hexylmethyl-dlchlorosilane with Na In refluxing toluene. A, on a deficit of Na B, with normal Na after 20% consumption of dichloride. 

Heat Test A rapid stability test depending on detection of traces of products of decomposition of an explosive at an elevated temperature. In Britain this usually refers to the Abel Heat Test. 

Microwave irradiation at solvent-free conditions induces pyrazoyl 2-azadienes to undergo Diels-Alder reactions with nitroalkenes, within 5-10 min good yields of pyrazolo[ 3,4-b pyridine s are obtained (see Eq. 8.25).39 Without irradiation the reaction produces only traces of products on classical heating. 

Furthermore, the addition of dichlorocarbene to ene-ynes proved to be remarkably sensitive to substituent effects. Trans-1,4-diphenyl butenyne gave only the cyclopropenone 17 via hydrolysis of dichlorocyclopropene 16, however, 2-methyl-pentene-l-yne-3 favored the formation of the dichlorocyclopropane 18 with only traces of products resulting from addition to the triple bond ... 

In most other cases, however, the diene system simply becomes too unreactive to participate in radical chain reactions. Thus, the reductive decarboxylation of ester 7 by Barton-POC ester methodology20 or as the selenoester21 gives the reduced product 8, cleanly without any trace of product in which the diene system has participated in the reaction (equation 4)20-21. 

Figure 6. HPLC kinetics of polygalacturonic acid depolymerization by extracellular pectate lyases from crude supernatants of Erwinia chrysanthemi and Lachnospira multiparus cultures. A panels are full scale representations of products found over the reaction time sequence. B panels have expanded ordinates to better demonstrate the kinetics of minor products. Area unit refers to integration from HPLC tracings of product absorbance at 235 nm. Numbers in the panels refer to the degree of polymerization for individual products. Conditions for enzyme assay and product detection were the same as described for Figure 5.

In Hght of the hahde effects, the role of the copper afkoxide and the lithium halide, derived from the transmetaUation, was probed by preparing the copper afkoxide under salt-free conditions (Tab. 10.10) [24, 51, 52]. Initially, mesityl copper, from which the metal hahde salts are removed during preparation [53], was chosen to provide the copper(I) afkoxide. Interestingly, only a trace of product was observed in the absence of hthium... 

The cleanest product composition may be effected by decomposition of the pure hydroperoxide or solutions in the injection block of the gas chromatograph. In carbon tetrachloride solution only methyl vinyl ketone and methyl vinyl carbinol were produced, the ratio of ketone to alcohol being 2.9. No definite traces of products from isomerized hydroperoxide were observed. 

Figure 8 shows representative GPC (RI) traces of products obtained before (Fig. 8a) and after (Fig. 8b) St addition. The star block was prepared by two incremental IB additions followed by the addition of St. The crossover from PIB to PIB-St was marked by a color change from pale yellow to deep orange on the addition of St. The charge was homogeneous throughout the polymerization with a gradual viscosity increase after St addition. After quenching and precipitating with methanol, the products were redissolved in MeCH and digested with 5% HCl (to remove coinitiator residues) and methanol. Star blocks thus obtained were readily soluble in THF and were purified by reprecipitating from methanol.

Fig. 8. GPC (RI) traces of products obtained a before St addition b after St addition...

Figure 11 shows representative GPC (RI) traces of products obtained before and after pClSt addition. The sharp peaks at -30 and -29 ml, respectively, correspond to (PIB)3-C8 and (PpClSt-b-PIB)3-C8 and the minor peaks are due to side products. The small peak (-12% by RI peak area) at -34 ml is due to the lin-... 

Fig.1l. GPC (RI) trace of products a before pClSt addition ((PIB)g-C8) b after pClSt addition [(PpClSt-b-PIB)8-C8]...

The 1-alkynyl (0.55 mole) is added in 5 min to a solution of 0.50 mole of lithium dialkylamide in 500 ml of ether at room temperature. The ether is removed by distillation and an exothermic reaction starts at a bath temperature of about 80°C. Heating is continued for an additional 30 min at 110°-120°C and then the reaction products are distilled at 15 mm Hg pressure using a short Vigreux column. The heating bath is raised to 170°C and the last traces of products are removed by distillation at 1 mm Hg pressure. In all cases the distillation receiver should be cooled to —80°C. The entire distillates are combined and fractionated through a 30 cm Widmer column. Some typical results of using this method are shown in Table II. 

In their original paper, Sieger and Calvert proposed the second of these routes as the predominant primary step. This is unlikely to be the case because no trace of products which could arise by the reactions of the trifluoroacetyl radical have been observed in the photolysis of either trifluoro- or hexafluoroacetone and it is assumed that this radical is unstable. In support of this is the evidence that the yield of ethane rises steadily with increase in temperature whereas that of hexafluoroethane remains approximately constant. Finally, in a recent re-investigation, Dawidowicz and Patrick49 have identified biacetyl in the products of the photolysis of trifluoroacetone. The most probable primary step is, therefore, the former, which provided the acetyl radical and a trifluoro-methyl radical. 

No traces of products which could arise from the intervention of the chlorodifluoroacetyl radical were observed, although it is possible that these were too involatile to be detected. This suggests that the primary step is of type B where chlorodifluoromethyl radicals and a molecule of carbon monoxide are produced. 

Reduction of the 7-iodo- and 7-bromo-aminochromes with this reagent gives more complex mixtures of products. The reduction process is accompanied by a considerable amount of dehalogenation in each case, and both the expected halogeno-5,6-dihydroxyindole and the corresponding 5,6-dihydroxyindoles are produced.155 Traces of products, similar to the unidentified fluorescent product obtained from adrenochrome, were usually also detected chromatographically, together with several minor unidentified products.155... 

The complexes [Ni(CO)3PPh3] and [NiCl2(PPh3)2] were less active, and [NiCl2(diphos)] gave only traces of product. The basic steps of the mechanism are given in Scheme 35. 

Whereas compound 7, as previously noted, is extremely sensitive to hydrolysis, it is actually rather difficult to cleave the NX)-acetal in the u-alkylated product 24. Use of aqueous hydrogen bromide as suggested by Setback 1 leads to only traces of product, although the desired result is achievable with dilute sulfuric acid... 

From the reaction of the methanol-ethanol mixture with freshly prepared catalyst, 98% of the products was trapped in the two traps cooled in a dry ice-isopropyl alcohol bath. The third trap containing 2-(2-meth-oxyethoxyjethanol cooled in a dry ice-isopropyl alcohol bath showed only traces of several products. Therefore, it was assumed that the remaining 2% of the material was gaseous products, as observed in previous reactions. In addition to the products described in Table 7, formaldehyde (1.75 mmol) and acetaldehyde (0.57 mmol) were also identified. When the same reaction was carried out with the used catalyst, almost 100% of the products was trapped in the first two traps. The third trap showed only traces of product as before. Other products were formaldehyde (0.39 mmol) and acetaldehyde (0.25 mmol). 

However, they encountered a problem with the purification of 220 from the by-product, triphenyl phosphine oxide and therefore developed an alternative route for the cyclization. Thus, treatment of 219 in dichloromethane with 1.5equiv of methanesulfonyl chloride and 3equiv of TEA gave traces of product 220 along with O-mesylated intermediate 221 as the major product (Equation 27). 

Figure 12 Cage effect during the photolysis of dibenzyl ketone. Top GC traces of products in micelles and solution. Bottom Cage effect with respect to the detergent concentration. Note the sudden change in the cage effect at the cmc.

A different domino reaction yet involving rather similar steps, i.e. car-bopalladation of an allene and nucleophilic attack of a phenol, was elaborated by the same group and leads to isoxazolidines 138 after intramolecular cycloaddition in the intermediates 137 [81] (Scheme 21). This transformation was performed with several aryl and hetaryl iodides 48 and gave the highest yields with electron-rich aryl iodides while only traces of products were obtained starting from electron-deficient aryl iodides. 

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