Benzenes alkenes

Cumene is generated following a deprotonation step [85]. One of the undesired reactions is multiple alkylahon with propylene. Oligomerization of propylene is also undesired. Beta zeolite is a typical catalyst for this reaction. A series of Beta zeolites synthesized with Si/Af rahos ranging from 20 to 350 were evaluated for the alkylation of benzene with propylene at 423°K and 3 MPa in the presence of benzene alkene molar raho of 7.0. The benzene alkene molar ratio was kept high in order to minimize the undesired reactions. The selectivity to the mono-alkylate product was 92-93% in every case with the balance being the dialkylated product. The activity decreased with increase in Si/Al2 but the selectivity was independent of the Si/A12 ratio [86]. 

The irradiation of benzenes with alkenes provides a fascinating array of photochemical reactions, not least because it converts the aromatic substrates into polycyclic, non-aromatic products. In principle, benzene can undergo reaction across the 1,2-(ortho). 1,3-(meta), or 1,4-(para) positions the 1,3-cycloaddition is structurally the most complex, but it is the predominant mode of reaction for many of the simplest benzene/alkene systems. The products are tricyclic compounds with a fusion of two five-membered rings and one three-membered ring, and an example is the reaction of benzene with vinyl acetate (3.411. For monosubstituted benzenes there can be a high... 

The isomeric cage products 248-250 are formed from 247 via intramolecular benzene-alkene photocycloadditions between chloranil and 1,1-diarylethenes, induced by the triplet excited enedione moiety [283] (Scheme 69). 

The second product (21) in the reaction of the diester (equation 70) results from 1,3-addition to the aromatic ring. Such addition is the major mode of reaction for benzene/alkene photocycloadditions, but with alkynes it is less common. One of the few reported examples is the addition of diphenylacetylene to esters of trimesic acid (equation 71),... 

The direct action of elemental sulfur on organic compounds in the presence of bases provides a general method of sulfuration that often results in a complex mixture of products.3,4 Sulfur has been extensively used in the dehydrogenation of saturated compounds thus, alkanes by heating with sulfur above 200°C yield unsaturated products for instance, in this way, cyclohexane is converted to benzene. Alkenes are generally much more reactive than alkanes and often react at 130°C for instance, methylcydohexene (1) yields the dithiathiones (2) and (3) (Scheme 1). 

In Chapter 15, we will examine the structural features that cause a compound to be aromatic. We will also look at the features that cause a compound to be antiaromatic. Then we will take a look at the reactions that benzene undergoes. You will see that although benzene, alkenes, and dienes are all nucleophiles (because they all have carbon-carbon rr bonds), benzene s aromaticity causes it to undergo reactions that are quite different from the reactions that alkenes and dienes undergo. 

Remarkable also is the related case of the meta benzene-alkene cycloaddition. Here again, mixtures are formed, but at least when the alkene moiety is tethered to the benzene ring and a preferred conformation exists, regio-selective processes have been found where several new stereocentres are formed in a single step and in a rigorously controlled way—and thus are synthetically highly valued (see Scheme 2.5) [15]. 

Chapter 19 focuses on the reactions of benzene and substituted benzenes. Although benzene, alkenes, and dienes are all nncleophiles (becanse they all have carbon-carbon tt bonds), benzene s aromaticity causes it to react in a way that is qnite different from the way alkenes and dienes react You will see how a substituent can be placed on a benzene ring and some reactions that can change the substiment after it is on the ring. You will also learn how a substituent affects both the reactivity of a benzene ring and the placement of an incoming snbstituent Chapter 19 also describes two additional types of reactions that can be used to synthesize snbstituted benzenes the reactions of arene diazonium salts and nucleophilic aromatic substitution reactions. 

Let s look at the splitting patterns and coupling constants of the benzene/alkene protons for more clues. Measuring the coupling constants for each resonance provides the values listed in the following summary table. 

Arosolvan process A process for the extraction of benzene and toluene from a mixture of aromatic and saturated hydrocarbons using a mixture of water and N-methylpyrrolidone. The process is used when naphtha is cracked to produce alkenes. To prevent extraction of alkenes these are saturated by hydrogenation prior to extraction. 

Over the past decade it has been established that for various substituents the i C chemical shift increment is a constitutive property. This applies to many systems e.g. benzenes, alkanes and alkenes. The availability of over 200 allenes, randomly substituted with groups of different nature, enabled us to prove that in the case of allenes the chemical shift increment is a constitutive property too, thus establishing a convenient method for estimating i ( C) values for allenes. 

The first report of oxidative carbonylation is the reaction of alkenes with CO in benzene in the presence of PdCh to afford the /3-chloroacyl chloride 224[12,206]. The oxidative carbonylation of alkene in alcohol gives the q, f3-unsaturated ester 225 and /3-alkoxy ester 226 by monocarbonylation, and succinate 111 by dicarbonylation depending on the reaction conditions[207-209]. The scope of the reaction has been studied[210]. Succinate formation takes... 

The Pd(II)-mediated reaction of benzene with alkenes affords styrene derivatives 259[230,231]. 

In addition to benzene and naphthalene derivatives, heteroaromatic compounds such as ferrocene[232, furan, thiophene, selenophene[233,234], and cyclobutadiene iron carbonyl complexpSS] react with alkenes to give vinyl heterocydes. The ease of the reaction of styrene with sub.stituted benzenes to give stilbene derivatives 260 increases in the order benzene < naphthalene < ferrocene < furan. The effect of substituents in this reaction is similar to that in the electrophilic aromatic substitution reactions[236]. 

Heteroaromatics such as furan, thiophene, and even the 2-pyridone 280 react with acrylate to form 281(244-246]. Benzene and heteroaromatic rings are introduced into naphthoquinone (282) as an alkene component[247]. The pyrrole ring is more reactive than the benzene ring in indole. 

Three oxidative reactions of benzene with Pd(OAc)2 via reactive rr-aryl-Pd complexes are known. The insertion of alkenes and elimination afford arylalk-enes. The oxidative functionalization of alkenes with aromatics is treated in Section 2.8. Two other reactions, oxidative homocoupling[324,325] and the acetoxylation[326], are treated in this section. The palladation of aromatic compounds is possible only with Pd(OAc)2. No reaction takes place with PdCl2. 

Dimethyl acetylenedicarboxylate (DMAD) (125) is a very special alkyne and undergoes interesting cyclotrimerization and co-cyclization reactions of its own using the poorly soluble polymeric palladacyclopentadiene complex (TCPC) 75 and its diazadiene stabilized complex 123 as precursors of Pd(0) catalysts, Cyclotrimerization of DMAD is catalyzed by 123[60], In addition to the hexa-substituted benzene 126, the cyclooctatetraene derivative 127 was obtained by the co-cyclization of trimethylsilylpropargyl alcohol with an excess of DMAD (125)[6l], Co-cyclization is possible with various alkenes. The naphthalene-tetracarboxylate 129 was obtained by the reaction of methoxyallene (128) with an excess of DMAD using the catalyst 123[62],... 

Ethyl /m s -2-butenyl sulfone (86) together with some ethyl vinyl sulfone are obtained by the reaction of ethylene and. SO2 in wet benzene using PdCl2. SO2 behaves mechanistically similarly to CO in this reaction[66]. Hydrosulfination of alkenes with SO2 and H2 is catalyzed by the Pd(dppp) complex. The sulfinic acid 87 is a primary product, which reacts further to give the. S-alkyl alkanethiosulfonates 88 as the major product, and 89 and the sulfonic acid 90 as minor products[67]. 

The classification of hydrocarbons as aliphatic or aromatic took place m the 1860s when It was already apparent that there was something special about benzene toluene and their derivatives Their molecular formulas (benzene is CgHg toluene is C7Hj ) indicate that like alkenes and alkynes they are unsaturated and should undergo addition reac tions Under conditions m which bromine for example reacts rapidly with alkenes and alkynes however benzene proved to be inert Benzene does react with Bi2 m the pres ence of iron(III) bromide as a catalyst but even then addition isn t observed Substitu tion occurs instead ... 

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