The main objective of the IPCS is to carry out and disseminate evaluations of the effects of chemicals on human health and the quality of the environment. Supporting activities include the development of epidemiological, experimental laboratory, and risk-assessment methods that could produce internationally comparable results, and the development of manpower in the field of toxicology.
Illustrative reactions[ edit ] The most widely practiced example of this reaction is the ethylation of benzene. Approximately 24, tons were produced in In this process, solid acids are used as catalyst to generate the incipient carbocation.
Many other electrophilic reactions of benzene are conducted, although on much smaller scale, they are valuable routes to key intermediates. The nitration of benzene is achieved via the action of the nitronium ion as the electrophile.
The sulfonation with fuming sulfuric acid gives benzenesulfonic acid. Aromatic halogenation with brominechlorineor iodine gives the corresponding aryl halides. This reaction Nitration of salicylic acid typically catalyzed by the corresponding iron or aluminum trihalide. The Friedel—Crafts reaction can be performed either as an acylation or as an alkylation.
Often, aluminium trichloride is used, but almost any strong Lewis acid can be applied. For the acylation reaction a stoichiometric amount of aluminum trichloride is required. Reaction mechanism[ edit ] In terms of the reaction mechanismthe aromatic ring attacks the electrophile A.
This step leads to the formation of a positively charged cyclohexadienyl cationalso known as an arenium ion. Many examples of this carbocation have been characterized, but under normal operating conditions they suffer loss of a proton from the methylene group.
Upon deprotonation, the pi system regains aromaticity. Effect of substituent groups[ edit ] Main article: Electrophilic aromatic directing groups Both the regioselectivity —the different possible arene substitution patterns —and the speed of an electrophilic aromatic substitution are affected by the substituents already attached to the benzene ring.
In terms of regioselectivity, some groups promote substitution at the ortho or para positions, whereas other groups favor substitution at the meta position.
These groups are called either ortho—para directing or meta directing, respectively. In addition, some groups will increase the rate of reaction activating while others will decrease the rate deactivating.
While the patterns of regioselectivity can be explained with resonance structuresthe influence on kinetics can be explained by both resonance structures and the inductive effect. Reaction rate[ edit ] Substituents can generally be divided into two classes regarding electrophilic substitution: Activating substituents or activating groups stabilize the cationic intermediate formed during the substitution by donating electrons into the ring system, by either inductive effect or resonance effects.
Examples of activated aromatic rings are tolueneaniline and phenol. On the other hand, deactivating substituents destabilize the intermediate cation and thus decrease the reaction rate by either inductive or resonance effects. They do so by withdrawing electron density from the aromatic ring.
The deactivation of the aromatic system means that generally harsher conditions are required to drive the reaction to completion.
An example of this is the nitration of toluene during the production of trinitrotoluene TNT. While the first nitration, on the activated toluene ring, can be done at room temperature and with dilute acid, the second one, on the deactivated nitrotoluene ring, already needs prolonged heating and more concentrated acid, and the third one, on very strongly deactivated dinitrotoluene, has to be done in boiling concentrated sulfuric acid.
Groups that are electron-withdrawing by resonance decrease the electron density especially at positions 2, 4 and 6, leaving positions 3 and 5 as the ones with comparably higher reactivity, so these types of groups are meta directors see below.
Such activating groups donate those unshared electrons to the pi system, creating a negative charge on the ortho and para positions. These positions are thus the most reactive towards an electron-poor electrophile. The highest electron density is located on both ortho and para positions,[ clarification needed ] although this increased reactivity might be offset by steric hindrance between substituent and electrophile.
The final result of the electrophilic aromatic substitution might thus be hard to predict, and it is usually only established by doing the reaction and determining the ratio of ortho versus para substitution.
In addition to the increased nucleophilic nature of the original ring, when the electrophile attacks the ortho and para positions of aniline, the nitrogen atom can donate electron density to the pi system forming an iminium iongiving four resonance structures as opposed to three in the basic reaction.
This substantially enhances the stability of the cationic intermediate. When the electrophile attacks the meta position, the nitrogen atom cannot donate electron density to the pi system, giving only three resonance contributors. This reasoning is consistent with low yields of meta-substituted product.
Other substituents,such as the alkyl and aryl substituentsmay also donate electron density to the pi system; however, since they lack an available unshared pair of electrons, their ability to do this is rather limited.
Thus, they only weakly activate the ring and do not strongly disfavor the meta position. Directed ortho metalation is a special type of EAS with special ortho directors.
Meta directors[ edit ] Non-halogen groups with atoms that are more electronegative than carbon, such as a carboxylic acid group CO2H draw substantial electron density from the pi system.
These groups are strongly deactivating groups. Therefore, these electron-withdrawing groups are meta directing.I want to extract soil nitrogen using KCL and use IC for analysis of Nitrate. In most of the protocols that I found so far 1 M KCL is used for extraction.
of acetylsalicylic acid Results and Data treatment (A) Preparation of aspirin i) Details about the reactants Reaction of the acetylation of salicylic acid is following From the balanced reaction above, it can be seen that the stoichiometry between salicylic acid and acetic anhydride is 1: 1.
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Salicylic acid also called the 2-Hydroxybenzoic acid is a benzene ring that has an alcohol and a carboxylic acid in an ortho position. Upon the nitration of the salicylic acid, para product is the. Runaway phenomena and thermal explosions can originate during the nitration of salicylic acid by means of a nitric acid/acetic acid mixture when the thermal control is lost, mainly as a result of the formation and thermal decomposition of picric acid.
Sulfuric acid (conc.) mL flask. Nitric acid (conc.) Stirring rod. Ice Mel-temp Water has a retarding effect on the nitration since it interferes with the nitric acid- Experiment 4: Nitration of Aromatic Compounds: Preparation of methyl-m-nitrobenzene Author.