Reduction of chlorobenzene to benzene

This page looks at the reaction of acyl chlorides acid chlorides with benzene in the presence of an aluminium chloride catalyst. This is known as a Friedel-Crafts acylation.

Acylation is the term given to substituting an acyl group such as CH 3 CO- into another molecule. An acyl group is a hydrocarbon group attached to a carbon-oxygen double bond. For UK A level purposes, the most commonly used example of an acyl group is the ethanoyl group, CH 3 CO- and so that's the one we will stick with throughout.

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So, if you react benzene with ethanoyl chloride in the presence of an aluminium chloride catalyst, the equation for the reaction is:. In the simplified formula for the product, the phenyl group is usually written on the left-hand side and the alkyl group to the right of the carbon-oxygen double bond - but I doubt if it really matters!

The aluminium chloride isn't written into these equations because it is acting as a catalyst. If you wanted to include it, you could write AlCl 3 over the top of the arrow. Ethanoyl chloride is added carefully to a mixture of benzene and solid aluminium chloride in the cold.

Hydrogen chloride gas is given off. Separating the product from the reaction mixture is fairly long-winded and beyond the scope of this site.

You may find slight variations on the temperature and time for this reaction. Friedel-Crafts acylation is a very effective way of attaching a hydrocarbon-based group to a benzene ring.

Although the product is a ketone a compound containing a carbon-oxygen double bond with a hydrocarbon group either sideit is easily converted into other things.

The carbon-oxygen double bond can be reduced to give a secondary alcohol, which in turn can undergo a whole lot of other reactions. That page doesn't deal specifically with this particular ketone, but the same principles apply.

This is known as the Clemmensen reduction and involves heating the ketone with amalgamated zinc a mixture of zinc and mercury and concentrated hydrochloric acid for a long time. It is possible to attach an alkyl group directly to the ring, but it is impossible to stop at substituting just one. An alkyl group attached to the ring makes the ring more reactive than the original benzene.

That means that something like ethylbenzene reacts faster than benzene itself. The result is that you get several ethyl groups substituted around the ring rather than just one. Attaching an acyl group to the ring makes the ring so unreactive that it won't substitute a second one.These metrics are regularly updated to reflect usage leading up to the last few days.

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Anaerobic microcosms were constructed using sediments from a historically chlorobenzene-contaminated site and were provided with yeast extract as an electron donor. In these methanogenic microcosms, all three isomers of dichlorobenzene DCB were reductively dehalogenated to monochlorobenzene MCB when added together or individually, with 1,2-DCB dehalogenation being the most rapid and 1,4-DCB the slowest.

When nearly all of the DCBs were consumed, benzene was detected and its accumulation was concomitant with MCB disappearance. Small amounts of toluene were also detected along with benzene. Subsequent doses of DCB or MCB were dehalogenated more rapidly than previous ones, consistent with a growth-related process.

Addition of a ca. These studies add to evidence that benzene production from chlorobenzenes needs to be considered when modeling processes at contaminated sites. View Author Information.

Cite this: Environ. Article Views Altmetric. Citations Abstract Anaerobic microcosms were constructed using sediments from a historically chlorobenzene-contaminated site and were provided with yeast extract as an electron donor.

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reduction of chlorobenzene to benzene

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Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts. The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online.

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The Role of Hydrogen Peroxide. Douglas E.Catalytic hydrogenation of aromatic rings requires forcing conditions high heat and hydrogen pressure.

Under milder conditions it is possible to reduce the double-bond of an alkene without reducing the aromatic ring.

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Recall the Friedel-Crafts alkylation from Section When attaching larger alkyl groups to arenes there is a possibility of rearrangement of the alkyl group structure. Although it does so less readily than simple alkenes or dienes, benzene adds hydrogen at high pressure in the presence of Pt, Pd or Ni catalysts.

The product is cyclohexane and the heat of reaction provides evidence of benzene's thermodynamic stability. Substituted benzene rings may also be reduced in this fashion, and hydroxy-substituted compounds, such as phenol, catechol and resorcinol, give carbonyl products resulting from the fast ketonization of intermediate enols.

Nickel catalysts are often used for this purpose, as noted in the following equations. Benzene is more susceptible to radical addition reactions than to electrophilic addition. We have already noted that benzene does not react with chlorine or bromine in the absence of a catalyst and heat.

In strong sunlight or with radical initiators benzene adds these halogens to give hexahalocyclohexanes. It is worth noting that these same conditions effect radical substitution of cyclohexane, the key factors in this change of behavior are the pi-bonds array in benzene, which permit addition, and the weaker C-H bonds in cyclohexane.

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The addition of chlorine is shown below on the left; two of the seven meso-stereoisomers are displayed to the right. Electrophilic nitration and Friedel-Crafts acylation reactions introduce deactivating, meta-directing substituents on an aromatic ring. The attached atoms are in a high oxidation state, and their reduction converts these electron withdrawing functions into electron donating amino and alkyl groups. Examples of these reductions are shown here, equation 6 demonstrating the simultaneous reduction of both functions.

Note that the butylbenzene product in equation 4 cannot be generated by direct Friedel-Crafts alkylation due to carbocation rearrangement. The zinc used in ketone reductions, such as 5, is usually activated by alloying with mercury a process known as amalgamation. Several alternative methods for reducing nitro groups to amines are known. These include zinc or tin in dilute mineral acid, and sodium sulfide in ammonium hydroxide solution.

The procedures described above are sufficient for most cases. Another way of adding hydrogen to the benzene ring is by treatment with the electron rich solution of alkali metals, usually lithium or sodium, in liquid ammonia. See examples of this reaction, which is called the Birch Reduction. The Birch reduction is the dissolving-metal reduction of aromatic rings in the presence of an alcohol. To remedy these limitations, a new and improved reaction was devised: The Friedel-Crafts Acylation, also known as Friedel-Crafts Alkanoylation.

The very first step involves the formation of the acylium ion which will later react with benzene:. The second step involves the attack of the acylium ion on benzene as a new electrophile to form one complex:.

The third step involves the departure of the proton in order for aromaticity to return to benzene:. During the third step, AlCl 4 returns to remove a proton from the benzene ring, which enables the ring to return to aromaticity.

In doing so, the original AlCl 3 is regenerated for use again, along with HCl. Most importantly, we have the first part of the final product of the reaction, which is a ketone.

reduction of chlorobenzene to benzene

Thie first part of the product is the complex with aluminum chloride as shown:. Because the acylium ion as was shown in step one is stabilized by resonance, no rearrangement occurs Limitation 1.

Also, because of of the deactivation of the product, it is no longer susceptible to electrophilic attack and hence, is no longer susceptible to electrophilic attack and hence, no longer goes into further reactions Limitation 3. However, as not all is perfect, Limitation 2 still prevails where Friedel-Crafts Acylation fails with strong deactivating rings. How would you make the following from benzene and an acid chloride? Steven Farmer Sonoma State University.

Objectives After completing this section, you should be able to write an equation to represent the reduction of a substituted benzene to a substituted cyclohexane. Specify all reagents, the structure of the intermediate ketone, and the necessary starting material.The chief products are phenol and diphenyl ether see below.

reduction of chlorobenzene to benzene

This apparent nucleophilic substitution reaction is surprising, since aryl halides are generally incapable of reacting by either an S N 1 or S N 2 pathway. The presence of electron-withdrawing groups such as nitro ortho and para to the chlorine substantially enhance the rate of substitution, as shown in the set of equations presented below. To explain this, a third mechanism for nucleophilic substitution has been proposed. This two-step mechanism is characterized by initial addition of the nucleophile hydroxide ion or water to the aromatic ring, followed by loss of a halide anion from the negatively charged intermediate as illustrated below.

The sites over which the negative charge is delocalized are colored blue, and the ability of nitro, and other electron withdrawing, groups to stabilize adjacent negative charge accounts for their rate enhancing influence at the ortho and para locations.

Three additional examples of aryl halide nucleophilic substitution are presented below. Only the 2- and 4-chloropyridine isomers undergo rapid substitution, the 3-chloro isomer is relatively unreactive.

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Nitrogen nucleophiles will also react, as evidenced by the use of Sanger's reagent for the derivatization of amino acids. The resulting N-2,4-dinitrophenyl derivatives are bright yellow crystalline compounds that facilitated analysis of peptides and proteins, a subject for which Frederick Sanger received one of his two Nobel Prizes in chemistry. Such addition-elimination processes generally occur at sp 2 or sp hybridized carbon atoms, in contrast to S N 1 and S N 2 reactions.

When applied to aromatic halides, as in the present discussion, this mechanism is called S N Ar. Some distinguishing features of the three common nucleophilic substitution mechanisms are summarized in the following table. There is good evidence that the synthesis of phenol from chlorobenzene does not proceed by the addition-elimination mechanism S N Ar as previously described.

However, ortho-chloroanisole gave exclusively meta-methoxyaniline under the same conditions. These reactions are described by the following equations. The explanation for this curious repositioning of the substituent group lies in a different two-step mechanism we can refer to as an elimination-addition process. The intermediate in this mechanism is an unstable benzyne species, as displayed in the above illustration by clicking the "Show Mechanism" button.

In contrast to the parallel overlap of p-orbitals in a stable alkyne triple bond, the p-orbitals of a benzyne are tilted ca. In the absence of steric hindrance top example equal amounts of meta- and para-cresols are obtained.It is a pale yellow solid.

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This reaction affords both the 2- and the 4-nitro derivatives, in about a ratio. These isomers are separated by distillation.

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Nitration gives 2,4-dinitrochlorobenzeneand 3,4-dichloronitrobenzene. Reduction with iron metal gives 4-chloroaniline.

4-Nitrochlorobenzene

The electron-withdrawing nature of the appended nitro-group makes the benzene ring especially susceptible to nucleophilic aromatic substitutionunlike related chlorobenzene. Thus, the strong nucleophiles hydroxide, methoxideand amide displace chloride to give respectively 4-nitrophenol4-nitroanisole, 4-nitroaniline. Another major use of 4-nitrochlorobenzene is its condensation with aniline to produce 4-nitrodiphenylamine. Reductive alkylation of the nitro group affords secondary aryl amines, which are useful antioxidants for rubber.

The National Institute for Occupational Safety and Health considers 4-nitrochlorobenzene as a potential occupational carcinogen that may be absorbed through the skin. From Wikipedia, the free encyclopedia. Redirected from 4-nitrochlorobenzene. CAS Number. Interactive image. PubChem CID. Chemical formula. Solubility in water. LD 50 median dose. LC 50 median concentration. PEL Permissible. REL Recommended. IDLH Immediate danger. Ullmann's Encyclopedia of Industrial Chemistry.

Weinheim: Wiley-VCH. Amsterdam, ; pp. Categories : Chloroarenes Nitrobenzenes. Namespaces Article Talk. Views Read Edit View history. By using this site, you agree to the Terms of Use and Privacy Policy. External MSDS. Lethal dose or concentration LD, LC :. Ca [1].This page only looks at one aspect of the chemistry of the aryl halides such as chlorobenzene - the fact that they are very unreactive compared with halogenoalkanes haloalkanes or alkyl halides. This is the only bit of their chemistry asked for by any UK A level syllabuses.

Preparation of Phenol From Chlorobenzene - Alcohols, Phenols and Ethers - Chemistry Class 12

A nucleophile can be either a negative ion or a molecule which carries a partial negative charge somewhere on it. On this page, we are just going to be looking at a simple nucleophile - a hydroxide ion. A nucleophilic substitution reaction is one in which a part of a molecule is replaced after it has been attacked by a nucleophile.

Follow this link to the introductory page on nucleophilic substitution reactions if you aren't absolutely confident about this. It would also be worthwhile looking at the page specifically about nucleophilic substitution by hydroxide ions. Both of these pages deal with nucleophilic substitution in the halogenoalkanes.

16.11: Reduction of Aromatic Compounds

The rest of this page is going to be a comparison with these reactions, and so it is important that you understand them. Here is a quick summary of the two ways that halogenoalkanes can react with hydroxide ions. We'll compare these with the aryl halides afterwards. The two different ways in which these reactions can happen depends on what kind of halogenoalkane you are talking about. Here is the mechanism for the reaction involving bromoethane - a primary halogenoalkane. A hydroxide ion attacks the slightly positive carbon atom and pushes off the bromine as a bromide ion.

Simple aryl halides like chlorobenzene are very resistant to nucleophilic substitution. In the lab, these reactions don't happen. There are two reasons for this - depending on which of the above mechanisms you are talking about.

The carbon-chlorine bond in chlorobenzene is stronger than you might expect. There is an interaction between one of the lone pairs on the chlorine atom and the delocalised ring electrons, and this strengthens the bond. Use the BACK button on your browser to return to this page if you follow this link. Both of the mechanisms above involve breaking the carbon-halogen bond at some stage. The more difficult it is to break, the slower the reaction will be.

This will only apply if the hydroxide ion attacked the chlorobenzene by a mechanism like the first one described above.

Sulphonation of benzene and nitration of nitrobenzene

In that mechanism, the hydroxide ion attacks the slightly positive carbon that the halogen atom is attached to. If the halogen atom is attached to a benzene ring, the incoming hydroxide ion is going to be faced with the delocalised ring electrons above and below that carbon atom.

The negative hydroxide ion will simply be repelled. If this is the first set of questions you have done, please read the introductory page before you start. Nucleophilic substitution reactions A nucleophile can be either a negative ion or a molecule which carries a partial negative charge somewhere on it.

reduction of chlorobenzene to benzene

Nucleophilic substitution in the halogenoalkanes Here is a quick summary of the two ways that halogenoalkanes can react with hydroxide ions. A tertiary halogenoalkane reacts differently. The mechanism this time involves an initial ionisation of the halogenoalkane:. Nucleophilic substitution in the aryl halides Simple aryl halides like chlorobenzene are very resistant to nucleophilic substitution.

The extra strength of the carbon-halogen bond in aryl halides The carbon-chlorine bond in chlorobenzene is stronger than you might expect.

Repulsion by the ring electrons This will only apply if the hydroxide ion attacked the chlorobenzene by a mechanism like the first one described above. That particular mechanism is simply a non-starter! Questions to test your understanding If this is the first set of questions you have done, please read the introductory page before you start.


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