Chemical yield

The amount of product produced when a reaction runs to completion is called the theoretical yield. The amount of actual product after a real experiment is the actual yield. As mentioned above, reactions often don t run to completion, and sometimes there are competing reactions that reduce the actual yield. Actual yield divided by the theoretical yield, times 100, gives the percent yield. 

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The chemical yield of hydrogen peroxide and the anthraquinone per process cycle is very high, but other secondary reactions necessitate regeneration of the working solution and hydrogenation catalyst, and the removal of organic material from the extracted hydrogen peroxide. 

Fig. 14. Chemical yield as a function of temperature for boron doped graphites.

Radiopltarrrujceutical Fluormatmg Agenf Synthesis Time (minf chemical Yield (%f Ref... 

The borane catalyst 4 is also effective in the Diels-Alder reaction of furan (Scheme 1.11). In the presence of a catalytic amount of this reagent a-bromoacro-lein or a-chloroacrolein reacts with furan to give the cycloadduct in very good chemical yield with high optical purity [6d]. 

Below is a table of asymmetric Diels-Alder reactions of a,/ -unsaturated aldehydes catalyzed by chiral Lewis acids 1-17 (Fig. 1.10, 1.11). The amount of catalyst, reaction conditions (temperature, time), chemical yield, endojexo selectivity, and optical purity are listed (Table 1.32). 

Several examples of catalytic aza Diels-Alder reactions using the chiral zirconium catalyst are shown in Table 5.5 [18]. High chemical yields and good to high... 

It was our delight that the reactions catalyzed were activated even at -40 °C in the presence of a catalytic amount of achiral titanium catalysts (10 mol%) to afford the desilylacetylated 2-pyrazoline cycloadduct Na, l-acetyl-4-methyl-5-(2-oxo-3-oxazolidinylcarbonyl)-2-pyrazoline, in high yields as the far major product (Scheme 7.35). Although some chiral titanium TADDOlate catalysts were successfully applied to activate these reactions leading to the moderate enantioselectivities (up to 55% ee), the chemical yields were not satisfactory. 

We employed malononitrile and l-crotonoyl-3,5-dimethylpyrazole as donor and acceptor molecules, respectively. We have found that this reaction at room temperature in chloroform can be effectively catalyzed by the J ,J -DBFOX/Ph-nick-el(II) and -zinc(II) complexes in the absence of Lewis bases leading to l-(4,4-dicya-no-3-methylbutanoyl)-3,5-dimethylpyrazole in a good chemical yield and enantio-selectivity (Scheme 7.47). However, copper(II), iron(II), and titanium complexes were not effective at all, either the catalytic activity or the enantioselectivity being not sufficient. With the J ,J -DBFOX/Ph-nickel(II) aqua complex in hand as the most reactive catalyst, we then investigated the double activation method by using this catalyst. 

As shown above, it was not so easy to optimize the Michael addition reactions of l-crotonoyl-3,5-dimethylpyrazole in the presence of the l ,J -DBFOX/ Ph-Ni(C104)2 3H20 catalyst because a simple tendency of influence to enantio-selectivity is lacking. Therefore, we changed the acceptor to 3-crotonoyl-2-oxazolidi-none in the reactions of malononitrile in dichloromethane in the presence of the nickel(II) aqua complex (10 mol%) (Scheme 7.49). For the Michael additions using the oxazolidinone acceptor, dichloromethane was better solvent than THF and the enantioselectivities were rather independent upon the reaction temperatures and Lewis base catalysts. Chemical yields were also satisfactory. 

The dsymmetnc Michael dclcliQon of 1,3-chcdrbonyl compounds to nitrostyrene is promoted by chiriil alkaloid catalysts to give the addition products in good chemical yield, but the enandoselecdvity is rather low fEq 4 47 ... 

The Michael acldiQon of formaldehyde hydra2Qne of fS -Tdmino-2-( methoxymethyl pyr-roLidine to nitroalkenes gives fi-nitrohydrazones in good chemical yield and stereoselectivity fEq 4 70 ... 

The Michael type reaction of f3/f -5-r-butyldimethysiloxy-3-phenyl-l//-pyrrolo[l,2-c oxa2ole with nitroethylene proceeds in the presence of Lev/is acid to give the alkylated product in good chemical yield and diastereoselecdvity In the case of nitroethylene, the Diels-Alder type transition state is favored to give the ryu-adduct selectively fEq 4 72 ... 

A careful assessment of the constitution of compound 10 led to the development of a rather efficient strategy featuring the Diels-Alder reaction (see Scheme 3). Although the unassisted intermole-cular reaction between 3-hydroxy-2-pyrone (16)23 and a,/ -unsatu-rated ester 17 is unacceptable in terms of both regioselectivity and chemical yield, compounds 16 and 17 combine smoothly in refluxing benzene and in the presence of phenylboronic acid to give fused bicyclic lactone 12 (61% yield) after workup with 2,2-... 

The transfer of an ethyl group, in particular, can be performed with high diastereoselectivity by the use of tetraalkyllead, activated with titanium(IV) chloride14"15 (Table 4). The order of addition of the reagents exhibits a strong influence on the chemical yield and diastercoselectiv-ity of the addition reaction. Typically, titanium(IV) chloride is added at -78CC to the aldehyde, followed by addition of tetraethyllead. Poor yields and diastereoselectivity are observed if titanium(IV) chloride is first added to tetraethyllead followed by addition of the aldehyde ... 

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