Working benzene

In the early work, benzene formed the basis of a variety of multi-armed structures. Analogs bearing from 2—6 arms were prepared and compared for cation binding ability. The only indication of mode of synthesis for the hexa-substituted benzene derivative is that it was obtained on reaction of benzene-hexakis(methanethiol) and l-bromo-3,6,9-trioxatridecane . The reaction is illustrated in Eq. (7.6), below, devoid of reaction conditions and yields which were not specified. 

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The important study of Berti et al. (also discussed in the context of the pinacol rearrangement see equations 8 to 11 of Chapter 3.2 in this volume) included BFs-induced reactions of the cis- and transepoxides (85 equation 36) and (91 equation 37), respectively. These very informative reactions show that, at least under the particular reaction conditions used in this work (benzene as solvent), the Coxon mechanism must be expanded to include an appreciable antiperiplanar geometrical feature. Unlike the pinacol rearrangements of the related diols, which gave only ketone (89) and aldehyde (90) under the same conditions, epoxide (85) gives, in addition to these same products, a significant amount of aldehyde (87). This appears to require the involvement of the twist boat conformer (86), which is the expected intermediate if the shown starting material conformer opens at the tertiary benzylic center with antiperiplanar constraints. Subsequent rotation of (86) to the chair conformer (88) allows formation of the ketone (89) and the aldehyde (90). 

In early work benzene was used as solvent (92), but later studies showed that the reactions proceeded equally well in iron pentacarbonyl (99). 

Note. For more delicate work, highly purified solvents are necessary, but for the above experiment dry technical benzene is suitable. 

Repeat the proeedure using HMO. HMO requires entry of the entire lower semimatrix, ineluding the diagonal and all zero elements. Beeause the matrix element format is II, only one symbol ean be entered for eaeh element. The numbers 0.5 and 1.2 eannot be entered in this format instead enter 1, whieh will be modified later. The initial unmodified input for pyridine is the same as that for benzene, 010010001000010100010 henee, we ean make a trial run on benzene to see if everything is working properly. 

Diethyl oxalate. Reflux a mixture of 45 g. of anhydrous oxalic acid (1), 81 g. (102-5 ml.) of absolute ethyl alcohol, 190 ml. of sodium-dried benzene and 30 g. (16-5 ml.) of concentrated sulphuric acid for 24 hours. Work up as for Diethyl Adipate and extract the aqueous laj er with ether distil under atmospheric pressure. The yield of ethyl oxalate, b.p. 182-183°, is 57 g. 

CHjO), + 3CH,OH + 3HC1 —> 3CH3OCH2CI + 3H,0 Monoalkyl benzene derivatives yield para chloromethjd compounds, frequently accompanied by small amounts of the ortho isomeride. The reaction is similar in some respects to that of Friedel and Crafts. Chloromethylation is of great value in synthetic work as the —CH,C1 group can be converted into other groups such as —CH,OH, —CHO, —CH,OR, —CH,CN, —CH,CH(COOC.,Hs)2 and —CH,. 

Ethyl benzyl ketone. Use 204 g. of phenylacetic acid (m.p. 77°) and 333 g. (335 -5 ml.) of propionic acid (b.p. 139-141°), but omit the extraction with benzene when working up the distillate. Distil the dried... 

Propiophenone. Prepare a solution of diphenyl-cadmium in 110 ml. of dry benzene using 4 9 g. of magnesium, 32 4 g. of bromobenzene and 19 5 g. of anhydrous cadmium chloride. Cool the solution to 10°, and add during 3 minutes a solution of 14 -8 g. of propionyl chloride (b.p. 78-79°) in 30 ml. of dry benzene use external coohng with an ice bath to prevent the temperature from rising above 40°. Stir the mixture for 2 hours at 25-35°. Work up the product as detailed above except that 6 per cent, sodium carbonate solution should replace the saturated sodium bicarbonate solution. The yield of propiophenone, b.p. 100-102°/16 mm., is 17 6 g. 

The most notable studies are those of Ingold, on the orienting and activating properties of substituents in the benzene nucleus, and of Dewar on the reactivities of an extensive series of polynuclear aromatic and related compounds ( 5.3.2). The former work was seminal in the foundation of the qualitative electronic theory of the relationship between structure and reactivity, and the latter is the most celebrated example of the more quantitative approaches to the same relationship ( 7.2.3). Both of the series of investigations employed the competitive method, and were not concerned with the kinetics of reaction. 

Nitration using this reagent was first investigated, by Francis. He showed that benzene and some of its homologues bromobenzene, benzonitrile, benzoyl chloride, benzaldehyde and some related compounds, and phenol were mono-nitrated in solutions of benzoyl nitrate in carbon tetrachloride anilines would not react cleanly and a series of naphthols yielded dinitro compounds. Further work on the orientation of substitution associated this reagent with higher proportions of o-substitution than that brought about by nitric acid this point is discussed below ( 5.3.4). 

Dewar and his co-workers, as mentioned above, investigated the reactivities of a number of polycyclic aromatic compounds because such compounds could provide data especially suitable for comparison with theoretical predictions ( 7.2.3). This work was extended to include some compounds related to biphenyl. The results were obtained by successively compounding pairs of results from competitive nitrations to obtain a scale of reactivities relative to that of benzene. Because the compounds studied were very reactive, the concentrations of nitric acid used were relatively small, being o-i8 mol 1 in the comparison of benzene with naphthalene, 5 x io mol 1 when naphthalene and anthanthrene were compared, and 3 x io mol 1 in the experiments with diphenylamine and carbazole. The observed partial rate factors are collected in table 5.3. Use of the competitive method in these experiments makes them of little value as sources of information about the mechanisms of the substitutions which occurred this shortcoming is important because in the experiments fuming nitric acid was used, rather than nitric acid free of nitrous acid, and with the most reactive compounds this leads to a... 

First-order nitrations. The kinetics of nitrations in solutions of acetyl nitrate in acetic anhydride were first investigated by Wibaut. He obtained evidence for a second-order rate law, but this was subsequently disproved. A more detailed study was made using benzene, toluene, chloro- and bromo-benzene. The rate of nitration of benzene was found to be of the first order in the concentration of aromatic and third order in the concentration of acetyl nitrate the latter conclusion disagrees with later work (see below). Nitration in solutions containing similar concentrations of acetyl nitrate in acetic acid was too slow to measure, but was accelerated slightly by the addition of more acetic anhydride. Similar solutions in carbon tetrachloride nitrated benzene too quickly, and the concentration of acetyl nitrate had to be reduced from 0-7 to o-i mol 1 to permit the observation of a rate similar to that which the more concentrated solution yields in acetic anhydride. 

Table 9.7 contains recent data on the nitration of polychlorobenzenes in sulphuric acid. The data continue the development seen with the diehlorobenzenes. The introduetion of more substituents into these deactivated systems has a smaller effect than predicted. Whereas the -position in ehlorobenzene is four times less reactive than a position in benzene, the remaining position in pentachlorobenzene is about four times more reactive than a position in 1,3,4,5-tetraehlorobenzene. The chloro substituent thus activates nitration, a circumstance recalling the faet that o-chloronitrobenzene is more reactive than nitrobenzene. As can be seen from table 9.7, the additivity prineiple does not work very well with these compounds, underestimating the rate of reaction of pentachlorobenzene by a factor of nearly 250, though the failure is not so marked in the other cases, especially viewed in the circumstance of the wide range of reactivities covered. 

The soiution is aliowed to cool and the crystals of the P2P-bisulfite addition compound are then separated by vacuum filtration, washed with a little clean dH20 then washed with a couple hundred mLs of ether, DCM or benzene. The filter cake of MD-P2P-bisulfate is processed by scraping the crystals into a flask and then 300mL of either 20% sodium carbonate solution or 10% HCi soiution are added (HCI works best). The soiution is stirred for another 30 minutes during which time the MD-P2P-bisulfite complex will be busted up and the P2P will return to its happy oil form. The P2P is then taken up with ether, dried and removed of the solvent to give pure MD-P2P. Whaddya think of that ... 

When completed, the solution is merely dumped into 1L of dH20 and extracted 3 x lOOmL Et20 or DCM or benzene. BUT when that solution hits the solvent, the biggest, ugliest emulsion Strike has ever hypothesized occurs. It is wicked The chemists can try all the usual tricks to get rid of that bitch, but when it comes down to it, there is only one way that works. The chemist is going to have to extract with hundreds upon hundreds of mLs of solvent. The idea here is to saturate both the aqueous and emulsion layer with so much solvent that a separate solvent layer can form. Once saturated, the entire mix can then be properly extracted. 

This procedure is called chloromethylation and will not only turn 1,3-benzodioxole into a methyl chloride but will work equally well in converting plain old benzene into benzyl chloride. Both are important stepping stones towards the production of X and meth. For example, benzyl chloride is a schedule I controlled substance because it will beget benzaldehyde and phenylacetonitrile (a precursor for phenylacetic acid). 

This is a nifty little way to turn catechol or guaiacol into protocate-chualdehyde or vanillin using what is called the Riemer-Tiemann reaction [137 p824, 138], It is a really ancient reaction and only works on benzene molecules that have an OH group. One needs to use KOH instead of NaOH because it is better at promoting para substitutions (don t ask). And if one is going to make vanillin from guaiacol then there needs to be a little ethanol in the reaction as well. 

This is the infamous Friedel-Crafts method and works in a manner similar to the previously mentioned method where P2P was made by merging benzene and chloroacetone using AICI3. This method is for speed makers only and is not recommended for conversion of 1,3-benzodioxole. However, this should work in a limited way on catechol. The conversion factor is very low but that isn t a major concern of speed chemists because cheap old benzene is the precursor and all of that benzene that isn t converted can be run back through this simple little process over and over again. Before she knows it, the chemist will have amassed an enormous amount of allylbenzene [139, 140]. 

There are a great many aspects to the Friedel-Crafts method that Strike does not have the space to go into. Friedel-Crafts works better if chloro or bromobenzene and their X counterparts are used in place of plain old benzene. Also, there is a significant amount of unwanted byproducts and molecular rearrangements that accompany this sort of reaction. Strike strongly suggests that people read more about this method before they attempt any such reaction. 

Note 2. Prepared by azeotropic removal of water from the commercial, water-containing product by means of benzene. This solvent was removed in a water--pump vacuum and the remaining mass was powdered. The water-containing acid appeared to work much less efficiently as catalyst. 

The structural facts that benzene is planar all of the bond angles are 120° and each car bon IS bonded to three other atoms suggest sp hybridization for carbon and the frame work of CT bonds shown m Figure 11 3a... 

Although all four tocopherols have been synthesized as their all-rac forms, the commercially significant form of tocopherol is i7//-n7i a-tocopheryl acetate. The commercial processes ia use are based on the work reported by several groups ia 1938 (15—17). These processes utilize a Friedel-Crafts-type condensation of 2,3,5-trimethylhydroquinone with either phytol (16), a phytyl haUde (7,16,17), or phytadiene (7). The principal synthesis (Fig. 3) ia current commercial use iavolves condensation of 2,3,5-trimethylhydroquiQone (13) with synthetic isophytol (14) ia an iaert solvent, such as benzene or hexane, with an acid catalyst, such as ziac chloride, boron trifluoride, or orthoboric acid/oxaUc acid (7,8,18) to give the all-rac-acetate ester (15b) by reaction with acetic anhydride. Purification of tocopheryl acetate is readily accompHshed by high vacuum molecular distillation and rectification (<1 mm Hg) to achieve the required USP standard. 

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