1. Unit Processes in organic Chemical Manufacturing
B.Sc. Industrial Chemistry
Semester 3
Jofrin J
Assistant Professor of Chemistry
T.M. Jacob Memorial Government College
Manimalakunu

4. Batch Nitration
Batch nitration is usually done in closed cast Fe or steel vessels. Modern practice uses mild C steel. Nitrator is an upright cylindrical vessel containing some cooling surfaces, an agitator, feed inlet and product outlet lines. Most nitrators are equipped with a large diameter quick dumping line for emergency use if the reaction gets out of hand or if the temperature rises because of failure of agitation, cooling or otherwise.

5. Continuous Nitration
Continuous nitration demands accurate metering and control equipment like positive displacement pumps, constant head orifice flow controls and rotameters. Schmid nitrator and Biazzi nitrator are the two common types of nitrators used in continuous nitration processes.

6. Merits and Demerits of batch and continuous nitrarion
Batch process
* Flexible
Capital cost is higher
Less safe
* Suitable for small scale production
Continuous process
Not Flexible
Capital cost is lower
More safe and efficent
Suitable for large scale production

7. SULPHONATION Chemical and physical factors in sulphonation
1. Concentration of SO3 in the sulphonating agent
2. Chemical structure of the organic compound
3.Time in relation to temperature and reagent strength
4. Catalysts
5. Solvents

8. 1. Concentration of SO3 in the sulphonating agent
It is necessary to maintain SO3 conc. in the sulphonating agent at a certain minimum level.
When SO3 is employed as the sulphonating agent, the conc. is maximum and initially the sulphonation is rapid and complete.
But sulphonic acid formed easily reacts with a second mole of SO3 to form a complex, which is less reactive than SO3.
So when reacting a hydrocarbon with SO3 on equimolar basis, one half of the hydrocarbon is sulphonated with SO3 and the other half is sulphonated by the less reactive complex.

9. Concentration of SO3 in the sulphonating agent………….
When using SO3 in H2O (H2SO4) as the sulphonating agent, as the conc. of H2O increases, the rate of sulphonation steadily decreases.
Sulphonation can be led to completion by the use of excess acid or by removing water physically or chemically.
Removal of water by physical method is done by distilling out water repeatedly from the reaction mixture.

10. 2. Chemical structure of the organic compound
Aromatic hydrocarbons are easily sulphonated.
The presence of activating groups like alkyl, – NH2, –OH etc facilitates the process of sulphonation
deactivating groups like –NO2, –COOH, – SO3H etc hinder sulphonation.

11. 3.Time in relation to temperature and reagent strength
To obtain maximum efficiency in sulphonation, the reaction time must be reduced to a minimum.
accomplished by:-
using a stronger sulphonating agent or
by raising the reaction temperature or
by using a large proportion of the reagent.

12. 4.Catalysts
The addition of catalysts can have a marked effect on some sulphonations.
Only a few catalysts are available for sulphonation, the best being I2 and salts of Hg, Ag and V.

13. 5.Solvents
The use of reaction solvents is essential and preferable to obtain efficient mixing and hence uniform reaction.
Excess acid can act as a solvent in sulphonation reactions.
Chlorinated solvents, liquid SO2, water, acetic acid, nitrobenzene, alcohols, pyridine, dimethylformamide etc are also used as solvents

14. Mechanism of aromatic sulphonation
Aromatic sulphonation is an aromatic electrophilic substitution reaction.
Four different species have been proposed to be the true sulphonating agent.
(i) H3SO4+
(ii) SO3
(iii) HSO3+ or
(iv) S2O6 (dimeric SO3).
Of these, SO3 is the strongest electrophile.

15. Mechanism of aromatic sulphonation
1. Generation of electrophile, SO3.
The sulfuric acid reacts with itself to form sulfur trioxide, the electrophile.
2. Formation of σ-complex
The SO3 is attracted to the π electron system of the benzene molecule to form a σ-complex

16. Mechanism.................. 3. Proton exchange
Loss of a proton re-establishes the aromaticity of the ring. The anion of benzenesulfonic acid is formed.

17. Mechanism
4. Formation of sulphonic acid

18. Batch Sulphonation
production occurs in time-sequential steps in batches.
A batch of feedstock(s) is fed into a process or unit, then the chemical process takes place, then the product(s) and any other outputs are removed.
production may be repeated over again and again with new batches of feedstock.
Batch operation is commonly used in smaller scale plants such as pharmaceutical or specialty chemicals production.

19. Continuous sulphonation
In continuous operation, all steps are ongoing continuously in time.
the feeding and product removal which together with the process itself, take place simultaneously and continuously. 

20. Batch Vs Continuous Small scale production Large scale production
Low process control
Improved process control.
Low quality product
Better product quality
Less efficient
More efficient
Equipment is simpler
Specialized equipment

21. Commercial sulphonation of alkyl benzenes (Toluene)
Sulphonation of toluene with conc. H2SO4 gives a mixture of ortho and para sulphonic acids
Temp. below 100°C favours the ortho product and temp. above 100°C favours the formation of the para isomer.

22. Sulphonation of toluene
Partial pressure distillation procedure is adopted for sulphonation.
For the sulphonation of alkyl benzenes, concentrated sulphuric acid is continuously pumped from the storage tank to the sulphonator.
Alkyl benzenes are also fed into the sulphonator. Both the reactants get reacted at the sulphonator.
The temperature is kept as required for the type of the isomer to be produced. Reaction time is usually about 1.5 hrs.
* This reaction can be done in both continuous and batch method.

23. HALOGENATION
defined as the process in which one or more halogen atoms are introduced into an organic compound.
Four types of halogenation
Fluorination,
Chlorination,
Bromination,
Iodination.

24. Halogenation may involve
Addition
Substitution of H atom by halogen
Replacement of groups like –OH and –SO3H

25. halogenation specific halogenating agent and a suitable catalyst
Many of the catalysts are halogen compounds of Fe, Sb,Hg, P etc.

26. CHLORINATION Direct action of chlorine gas
Hydrochloric acid as chlorinating agent
Sodium Hypochlorite (NaOCl)
Phosgene(COCl2)
Benzotrichloride(C6H5CCl3)
SOCl2
Sandmeyer reaction
Gatterman reaction

27. BROMINATION
Bromine, Bromides, bromates,alkaline hypobromates are used as brominating agents
Addition reactions
Replacement reactions
Substitution reactions

28. IODINATION
The methods employed in iodination differ somewhat from those chlorination and bromination.
The weak C–I bond makes permanent direct union of carbon to iodine by the replacement of hydrogen very difficult.
Iodinations are reversible in character.

29. Iodinating agents
Iodine
Hydroiodic acid
Alkali hypoiodites

30. Fluorination
Fluorine acts directly on hydrocarbons to produce fluorides, but the reaction is violent and explosive. F–F bonds are stronger than other halogens, but once the reaction is initiated and F atoms are available, they combine more readily with H and hydrocarbons than do the other halogens. The new bonds formed are very strong and the heat liberated is so great that precautions must be taken to control the reaction.

31. Fluorinating agents Vapours of fluorine HF
Alkali metal fluorides like NaF
Diazo reactions

32. Halogenation of aromatic side chain
When chlorine is passed into boiling toluene in presence of chlorine-activating light, a mixture of different chlorine products is obtained. The major product being those in which chlorine is substituted in the side chain.
A higher temperature ( °C) favours substitution in the side chain, while a lower temperature (30-50 °C) in the presence of a catalyst (eg: Fe or Al ) favours replacement of nuclear hydrogen.

33. Xylenes readily chlorinate in the side chain at high temperatures using chlorine-activating light. Meta and para xylene produce the hexachloride, but in o-xylene, the structure does not favour a sixth chlorine atom.

34. Chlorination of Benzene
Anhydrous benzene reacts with chlorine in presence of FeCl3 to give chlorobenzene at °C.
In the vapour phase, chlorine reacts with benzene at 500 °C to form of polychlorobenzenes. 1,3-dichlorobenzene is the major product, which further chlorinates to give symmetrical 1,3,5-trichlorobenzene.

35. Preaparation of some organo halogen compounds
1. CHLORAL , CCl3CHO
From ethanol
Ethyl alcohol, either absolute or containing water can be chlorinated to produce chloral

36. CHLORAL…. Chlorination of acetaldehyde
Acetaldehyde is chlorinated in presence of water to produce chloral.
CH3-CHO + 3Cl CCl3CHO +3HCl
One of the determining factors in the choice of the starting material is the disposal of the by-product hydrochloric acid. Acetaldehyde chlorination results in the formation of 3 moles of HCl per mole of chloral formed, but with ethanol, 5 moles of hydrochloric acid is formed. Another advantage is that only 3 moles of chlorine is consumed in the acetaldehyde chlorination as compared to the 4 moles used in the ethanol process.

37. DDT(1,1,1 trichloro-2,2-bis(p-chlorophenyl) ethane
It is produced when chloral or chloral hydrate is condensed with chlorobenzene in presence of H2SO4

38. BHC -Benzene hexachloride or hexachlorocyclohexane
When Benzene is chlorinated in the liquid phase in presence of an activating agent like an activating light, γ rays or elemental fluorine, a mixture of 5 isomers of 1,2,3,4,5,6- hexachlorocyclohexane is produced.

39. Chloro methanes
Direct halogenation of alkanes in the presence of light, heat or suitable catalyst gives haloalkanes.
Methane on reaction with Cl2 in presence of light gives chloromethane.
Chloromethane reacts with Cl2 to give dichloromethane, chloroform and carbontetrachloride.

40. Freon 12 : Dichlorodifluoromethane
The chlorofluoro derivatives of alkanes are commonly known as Freons. Dichlorodifluoromathane is known as Freon 12.
Freon 12 is prepared by the action of SbF5 on CCl4 in presence of SbCl5.
CCl4 + SbF CCl2F2+ 2SbCl3