03 Nitration u192k

Nitration

Addition of nitro-group by replacing a number of different monovalent atoms or groups of atoms, (especially hydrogen atom). 1-Nitro group attached to carbon atom (Nitroaromatic /nitroparaffinic compounds) C―NO2 2- Attached to oxygen atom(Nitrate ester) C―O―NO2 3-Nitro-group attached to nitrogen atom(Nitroamine/Nitroamide) N―No2

Nitration Products  

Solvents, dyestuffs, pharmaceuticals and explosives Also useful intermediates for the preparation of other compounds.

Nitrating agents: 

HNO3(fuming,concentrated,aqueous) Mixed acid(HNO3 & H2SO4)



HNO3 & acetic anhydride



HNO3 & acetic acid



Cont… 

HNO3 & phosphoric acid



HNO3 & chloroform



Nitrogen tetraoxide & pentaoxide NO2+ion: HNO3 exists in conc.H2SO4 (mixed acid) as nitryl ion. The nitration of aromatic compounds can be represented by the eqn: ArH+HNO3=ArNO2+H2O

  

Kinetics and Mechanism of Aromatic Nitration The Kinetics of nitration reaction depends upon the reaction medium (Aromatic compound and Nitrating agent etc.)  Let us first consider the reaction in a

strong H2SO4 medium.

 The rate of all aromatic nitration process

is proportional to the concentration of added nitric acid & of organic substrate .

Mathematically, this behavior can be

written as follows,

Rate α [HNO3] [ArH] Rate = K[HNO3] [ArH]

The most accepted mechanism process is regarded as follows, •

for

the

nitration

The organic compounds with intermediate reactivity show fractional dependence on the concentration of organic compound , the kinetics of the reaction are therefore, intermediate between zero and one.

• Various

mechanism proposed referred to above are as follows.

further

reactions

Cont… 

 

The effect of the amounts of H2O upon the rxn rate is that the rxn rate rises sharply with increasing content H2SO4 ration & reaches a maximum at about 90% H2SO4 & then falls off at higher acid concentration. The rise is due to increase in nitryl ion. Rxn mechanism in conc. H2SO4

Cont…   

HNO3+ 2H2SO4→NO2+ + H3O+2HSO4ArH + NO2→ArHNO2+ ArHNO2+ HSO4-→ArNO2+ H2SO4

1. Condition - A i. ii. iii.

HNO3 is in large excess. Deactivating group (NO+2) attached with nucleus of organic compound. Highly polar organic solvent such as sulfuric acid etc.

The mechanism is as follows, i. 2HNO3 H2NO+3 + NO-3 (Fast) ii. H2NO+3 H2O + NO+2 (Fast) iii. ArH + NO+2 ArNO2 + H+ (Slow) (R.D.S) • •

The First step (representing the transfer of a proton from one molecule of HNO3 to another )is very rapid. Rate of second step depends upon the medium.

•

Hence highly reactive aromatic compounds are nitrated at the same rate which is the rate of formation of nitryl ion.

• In the nitration of less reactive aromatic compounds,the formation of nitryl

ion is fast relative to the nitration step(RDS) •

Shows first order dependence on the organic substrate.

• Therefore, step – ii, involving the formation of nitronium ion (NO+2) should

be faster than reaction No. iii. On the basis of this mechanism, the rate expression conforms to the observed behavior.

2. Condition - B i.

HNO3 is in large excess.

ii.

Activating group (-CH3) attached with nucleus of organic compound.

iii.

Medium, Organic solvent.

For such reactions, the mechanism which could be compactable with to observed behavior is represented as follows, i.

2HNO3

H2NO+3 + NO-3 (Fast)

ii. H2NO3

H2O + NO+2 (Slow)

iii. ArH + NO+2

ArNO2 + H+ (Fast) (RDS)

3. Condition - C i.

Large excess of HNO3,

ii.

Organic compound containing average reactivity and medium containing organic solvent under these conditions, the reaction is thought to proceed via two paths.

a.

Independent of organic solvent (substrate)

b.

The other path is assumed as which does not involve the organic compound. The extent of any of two steps would have direct impact on the order of reaction.

Nitration in Organic Solvent With amount of HNO3 in large excess and in the presence of Organic solvent such as (non-aqueous) acetic acid, the kinetics of the nitration process depend directly on the Concentration of the organic compound. Thus when nitrobenzene ( NO 2) is nitrated in the presence of organic solvent. The system is 1st order w.r.t. organic compound. • It is thus clear that organic compounds possessing the deactivating groups (e.g Nitrobenzene) show, the 1st order dependence.

• On the contrary, the organic compounds containing activating group (Toluene, Xylene) do not show any effect on the rate of reaction. The order of reaction for such system is zero. The rate of reaction with all substrate (organic compound) with zero order dependence has been found the same. This thing indicate that the rate determining step in all such nitration reactions is the same.

i.

HNO3 + 2H2SO4

NO+2 + H3O+ + 2HSO-4

ii.

ArH + NO2+

Ar HNO+2 (Intermediate)

iii.

Ar HNO+2 + HSO4 Ar NO2 + H2SO4

It has been observed that the rate of reaction rises sharply with increasing sulfuric acid concentration and reaches a maximum at about 90% H2SO4 and then falls off at higher acid concentration. •

The aspect of decrease in the rate of reaction with in the concentration of H2SO4 above 90% is however not explained by mechanism given above, except that the step No. (ii).

• It was first suggested that the rise in rate with increasing acid

strength when the acid is less then 90% is due to the increase in the concentration of nitrylion (NO+2). • A plausible explanation for the decrease in rate at higher acidity

(when H2SO4 > 90%) has been given by Gillespie and Millen. An interaction occurs between the organic substrate (e.g. nitrobenzene) and the sulfuric acid which decrease the electron density in the ring and hence decreases the reactivity. • The interactions is probably a hydrogen bond formation. •

The hydrogen bond between nitrobenzene and sulfuric acid can be pictured. O ArN

O - - HOSO3H The strength of a hydrogen bond increases with the acidity of the hydrogen donor, which is this case is sulfuric acid.

THE EFFECT OF ADDITION OF HNO2 IN NITRATION PROCESS Nitrous acid (HNO2) or Nitrogen Dioxide in certain instances exerts two types of effects, 1) 2)

Inhibiting effect catalytic effect INHIBITING EFFECT The inhibiting effect is observed in the nitration of compounds having no activating group; these reactions are necessarily carried out either in strong HNO3 or in mixed acids In this media nitrous acid forms nitrosyl ion (NO)+ HNO2 + HNO3 HNO2 + 2H2SO4

NO-3 + NO+ + H2O H3O+ + 2HSO-4 + NO+

So, nitrosyl ion decreases the concentration of nitryl ion and thus reduces the reaction rate. CATALYTIC EFFECT: The catalytic effect is observed in the nitration of reactive substrate such as anisole (Methyl Phenyl ether (CH3OC6H5) or dimethl aniline, which is nitrated, in weak acid where nitryl ion concentration in low. The catalysis is due to the formation of nitroso compound, which is oxidized to nitro compound. ArH + NO+ ArNO + HNO3

ArNO + H+ ArNO2 + HNO2

Because nitrosyl ion is much weaker electrophonic reagent than nitryl, ion is able to react only with very reactive aromatic compounds such as anisole or dimethylaniline. Two conditions are necessary for catalysis by HNO2. 1)

The substrate must sufficiently reactive to attack by nitrosyl ion.

2)

The reaction mediums have concentration of nitryl ion very low thus allowing the nitrodyl ion to compete favorably for substrate. OXYNITRATION An interesting reaction occurs between benzene and approximately 50 percent nitric acid containing 0.2 molar mercuric nitrate which yields up to 85 percent dinitrophenol and picric acid. This process is known as oxynitration.

NITRATION OF PARAFFINIC HYDROCARBONS Gas Phase Reaction In contrast to aromatic hydrocarbons, which are susceptible to attack by electrophilic reagents such as the nitryl ion, the paraffins are quite inert to such reagents. The paraffins, on the other hand, are susceptible to attack by certain atoms and free radicals. The nitration of these compounds are practiced commercially is carried out in the vapor phase and at temperature of 350 – 450 °C; it is undoubtedly a free radical reaction. Nitric Acid of 70% strength or less is generally used, although Nitrogen Dioxide can also be used. A characteristic feature of reactions involving alkyl radicals is the great variety of product formed. This is clearly shown by the nitration of 2 – methyl pentane which yields all the possible mononitrations products that might be formed by breaking any one of bonds present and introducing a nitro group at the pint of cleavage.

The products are:1) Nitro methane 2) Nitro ethane 3) 2 – nitro propane 4) 2 – nitric butane 5) 1 – nitro isobutene 6) 1- nitro – 3 – methyl butane 7) 2- nitor-3-methylbutane

The nitration produces only mononitroparaffins and no significant amounts of polynitro compounds. Although cleavage of the carbon skeleton occurs, as shown above, on rearrangement of the carbon skeleton has been found to occur.

The reaction is carried out by ing the reactants through the reaction chamber in a flow system. The products are condensed and distilled. As a result of a systematic study, the following facts have emerged. 1)

There is an optimum temperature at which the highest yield is obtained. Using butane and concentrated nitric acid is molar ratio of 15:1, and a time of 1.6 sec, the result shown in the accompanying table were obtained. Temperature °C % Conversation of nitric acid % Yield of RNO2 based on butane

2)

405 15 1

425 36 2.9

435 22 1.4

The addition of oxygen increases the yield based on nitric acid but also increases the oxidation of butane. The effects are shown in fig. oxygen also increase the yield of nitro methane and nitro ethane and decreases the yield of nitro butane.

3)

Nitrogen dioxide also reacts with paraffins to yield nitroparaffins. At 325 °C, a time of 1.9 min, and propane: NO 2 = 4.2, the percent conversion of NO2 is 16.6 and the yields based on the moles of hydrocarbons is 51 percent. The addition of oxygen lowers the optimum temperature and improves conversion and yields. At 285 °C, time 3 min, and O2 : NO2 = 0.75, the conversion is 29 percent and the yield is 71 percent.

4)

Bromine has a beneficial effect on both yields and conversions to nitroparaffins using nitric acid. At 423 °C, a time of 1.5 sec, and the following rations of reactants, propane: O2 = 8.2, propane: nitric acid = 9.9, water: nitric acid = 15 and Br2:HNO3 = 0.015, the percent conversion of nitric acid is 47.7 and the yield based on propane is 55.5 percent. The yield of other products are follows: CO 2 = 0, CO = 3.6, C3H6 = 9.7, C2H4 = 4.1, aldehydes and ketones = 27 percent. The effect of chlorine is similar to that of the bromine.

5)

Highly branched hydrocarbons undergo less fission during nitration than they do their less branched isomers. Correspondingly, hydrogen substitutions are favored when highly branched structure is nitrated. As can be seen from the data in table, in which ha comparison is made of the nitration of isomeric butanes and pentanes the molar ratio of the product resulting from fission so that resulting from hydrogen substitutions decreases as the carbon skeleton becomes more highly branched.

Hydrocarbons fission products

Temp °C

Mole% of Products

Ratio

substitution products

Butanes

420

10.5 15.8 5.3 44.2 24.2

nitro methane nitro ethane 1-nitroprepane 2-nitrobutane 1-nitrobutane

0.463

2-Methylpropane

420

5.8 23.1 7.0 64.1

nitro methane 0.407 2-nitropropane 2-methyl, 2-nitrobutane 2-methyl, 1-nitrobutane

N-Pentane

400

2-Methylbutane

420

2,2-Demethylpropane

410

2.3 10.9 16.7 12.8 18.9 18.2 20.2 3.9 8.8 16.1

nitro methane nitro ethane 1-nitroprepane 1-nitrobutane 1-nitropentane 2-nitropentane 3-nitropentane nitro methane nitroethane 2-nitropropane

0.475

9.8 12.2 14.0 24.1 11.1 14.0 13.0 73.0

2-nitrobutane 2-methyl-2-nitrobutane 3-methyl-2-nitrobutane 2-methyl-1-nitrobutane 3-methyl-1-nitorbutane nitro methane 0.370 2-methyl-2-nitropropane

0.628

2-methyl, 1-nitropropane

2,2-dimethyl1-1-nitropropane

The benzene is initially converted to phenyl mercuric nitrate which reacts with nitrogen dioxide to yield nitrosobenzene. Each of these intermediates has been isolated from the reaction mixture. The nitrosobenzene can react in two ways. In nitric acid weaker than 50 percent, it reacts with 2 moles of nitric oxide to form phenyldiazonium nitrate, a reaction first discovered by Bamberger. The diazonium salt is converted by water to phenol, which is nitrated in steps to the final products. In nitric acid of greater than 50 percent concentration, the nitrosobenzene is converted directly to p-nitro phenol without going through the diazonium compound. The p-nitro phenol is then nitrated further to give the dinitrophenol and picric acid.

N-NITRO COMPOUNDS The n-nitro compounds include the nitramines, which have the structure (A), and the nitramides, which have the structure (B). NO2

NO2

(A)

(B) R

N

R’

RCO

N

R’

Where R is an alkyl or aryl group and R’ is H, alkyl or aryl. The primary nitramides are those in which R’ is H. N-nitro compounds find their greatest use as explosives and propellants. Trimethylenetrinitramine, which is known as RDX, is used as an explosive as is 2,4,6 trinitro – N-nitro – N-methyl aniline, which is known as tetryl. Nitroguanidine is used in solid propellant formulations.

H2

H 3C

N

NO2

L

O2N

N

N

NO2

O 2N

NO2 NH

H2C

CH2 H 2N

NHNO2 N NO2

RDX

NO2 Tetryl Nitroguaidine

C

Methods of Preparation Primary nit amines can not be prepared by the direct, nitration of primary amines. Because of their sensitivity towards acid, they probably do not survive in the strongly acidic environment of the nitration. They are gently made by alkaline hydrolysis of nit amides. HNO2

RCORHCH2

OH

RCON(NO2)CH

RCOOH + HN(NO2) CH2

The nitramides are readily prepared by nitration of the amide with 100% nitric acid or with nitric acid, acetic anhydride, acetic acid mixture. Primary nitramines can also be prepared from the appropriate urethane. CICOOEt

CH2NH2

HNO 3

CH3NHCOOEt

NH 3

CH3(NO2)COOEt CH3NHNO2 + NH2COOEt

Secondary nitro mines are prepared by the nitrolysis of secondary amides or of N, N-dialkyl ureas. HNO2

RCON(CH3)2

RCOOH + (CH3)2 N NO2

RCNO

R2NH

HNO3

R2NCONH2 Dialhyl Urea

R2NNO2

Sec. Nitramine

Mr. G. W right and coworkers showed that nitramines could be obtained directly from secondary amines by using a nitrating mixture, which contains chloride ions. Thus by treating the amine nitrate with acetic anhydride containing zinc chloride, the nitramines of dimethylamine, diethylamine, piperdine and morholine were obtained in yields of 60-70 percent.

Aromatic nitramines undergo a rearrangement in which the nitro group migrates to the benzene ring. Such a rearrangements is believe to occur in the synthesis to tetryl, which is made by the nitration and nitrolysis of dimethylaniline with mixed acid. The reaction steps are as follows:H2C

N

CH2

CH2

N

CH2

NO2

H2C

N

NO2

NO2

H2C

N

H

NO2

H2C

N

NO2

NO2

The earlier process for making RDX consisted of reacting hexamine (hexamethylenetetramine) or its dinitrate salt with 98-100 percent nitric acid the yield of this method are not good because of the formation of RDX is accompanied by the formation of formaldehyde, which is oxidized by the nitric acid. Greatly improved yields (70-80%) can be obtained by means of the Bachman process, which employs hexamine, 98 percent nitric acid, ammonium, nitrate, and

Acetic anhydride. In the Bachman process a by product having the structure I also formed in yields up to 10%. The mechanism of these reactions is not thoroughly understood. CH2

CH2

N

N CH2

O2N

N

NO2 N

NO2

N

CH2

CH2 O2N

CH2

CH2

CH2

CH2

H 2C

N

N

NO2

CH2 CH2

N

CH2

N NO2 N

Hexamine

NO2

RDX

I

PROCESS EQUIPMENT FOR TECHNICAL NITRATIONS Types of Process Equipment 

Nitrations, as technical industrial processes, have evolved from bathtype operations using stoneware vessels and hand operations to automatically controlled continuous type processes carried out in gleaming stainless steal vessels.



The high heat of reaction and dilution involved in nitration, originally absorbed by the placing the stone ware vessels in a water bath, are now taken up by coils or jackets cooled by refrigerated brine.



Controls have evolved from none at all to completely automatic systems, which may be so elaborate as to permit operation from remote locations. The idea of remote control has always appealed to the designer of equipment for the manufacture of hazardous, explosive compounds, which often are result of nitration processes.

It will be convenient to discuss technical nitrations from the standpoint, 1st of bath processes and 2nd of continuous processes. This is the historical order of development. However it should not be concluded that batch processes have been rendered obsolescent by continuous ones or that they surely will be superseded. Each kind of process has advantages peculiar to itself. In broad , batch processes have the following advantages compared to continuous processes.

Flexibility: Batch process equipment possesses general usefulness because each batch of material ing through the process is separate, or nearly separate, from batches which have preceded or which will follow it. It is usually easier to introduce process variations into the batch process than into a continuous one. Furthermore, batch processing equipment is often of such general applicability that a given plant may be readily converted from production of one nitrated material to another. Beginning production of a new compound a pilot production

is conveniently done by the batch process by the operating flexibility, even through the use of a continuous process may be planned for the completely developed process.

Labor Usage: For high rates of production when large batches are used the labor efficiency of a batch process may be just as good as that for a continuous process. This appears to be true for the large scale industrial production of nitroglycerine and nitortoluene, for example:Continuous processes, in general will be found to have to following advantages over batch processes.

Lower Capital Costs: For a given rate of production, the equipment needed for a continuous process is smaller than for a batches process. This is usually the most striking difference between the two types of process.

The reason for this is obvious, Since it is not necessary to accumulate material in the continuous process anywhere, the vessels are designed with capacities dictated by the rate of reaction process step, which they much accommodate. Alternatively, because of the relatively small size of continuous process equipment, it is often possible and advantageous to use materials of construction, which would be excessively high in cost for batch scale equipment. Thus, for example, corrosion resistance alloys such as the appropriate stainless steels may be used for a continuous plant, whereas ordinary mild steal may be dictated for a batch plant because of cost. In the case of the stainless steel, corrosion problems may be completely eliminated. Safety: Because of the relatively small size of continuous process equipment, there is a less material in process at any time than at certain times in a comparable batch process. For example, at the completion of a batch process nitration and during its normal separation of the product from spent nitrating acid. The entire batch of an often hazardous compound will be present in the equipment. In the continuous process,

Only as much material needed to gain sufficient reaction or process time. In the case of high explosives made by nitration, such as nitroglycerine, this inherent safety factor of a continuous process is very attractive.

CONTINUOUS NITRATION WITH FORTIFIED SPENT ACID Methods for the continuous nitration of benzene have been proposed by Castner and Mares. Both processes are based on the recognition that a slightly HNO3- fortified spent acid constitutes a satisfactory nitrating agent for a limited quantity of hydrocarbon. To obtain volume production, it is necessary to circulate relatively large quantities of acid of low nitric acid content and high heat capacity and to remove the water of nitration continuously in an integrated evaporator operating under reduced pressures. When the heat of sulfuric acid hydration and the chemical heat of nitration are evolved in separate vessels by adding nitric acid to a prepared mixture of benzene, sulfuric acid, and water, the hazards of nitration are further reduced and it is feasible to operate safely at relatively high temperatures and to utilize the sensible heat in effecting the subsequent removal of water from the spent acid.

As shown in Fig. 4-14 the operation proceeds as follows:Hot sulfuric acid at 90 °C is run from the heat insulated storage tank (B) into one of a battery of nitrators (A1 to A4). Under vigorous agitation, sufficient 63 percent nitric acid is added to the nitrator to produce a mixed acid containing 4 percent HNO3. Sufficient benzene is then delivered from its storage scale tank to react with al the nitric acid in the nitrator. Upon completion of the reaction, which takes about 10 minutes, the agitation is stopped and the charge permitted to settle. While the separation of the nitrobenzene and spent acid proceeds, another nitration is started, thus providing a continuity of operations.

PREPARATION OF A-NITRO NAPHTHALENE NO2

+ HNO2

+ H 2O

When naphthalene is nitrated under optimal conditions, the product consists principally of α-nitro naphthalene. The reaction takes place vigorously; and unless precautions are taken, polynitro compounds are formed. If impure naphthalene is used, the nitration product will be unsatisfactory; and inasmuch as it is difficult to isolate α-nitro naphthalene in a pure state, it is advisable to prevent further complications and to use a pure raw material.

When the nitration is made without the use of cycle acid, a mixed acid of the following composition may be used: H2SO4 .…………… 59.55% HNO3 .…………….. 15.85% H2O .………………. 24.60% HNO3 ratio .………. 1.01 D.V.S. …………….. 2.04 This will yield a product consisting of 95 percent α-nitro naphthalene together with some unchanged naphthalene and very little dinitro derivative. By using cycle acid to dissolve the naphthalene to be nitrated an then proceeding with the nitration in the usual way, the operating steps are as follows: The naphthalene-1,280 Ib-is suspended, in 4,500 Ib of dilute sulfuric acid or spent acid containing about 65 percent H2SO4. The whole is thoroughly stirred, and 2,350 Ib of mixed acid of the following composition is slowly added:

H2SO4 .…………… 56.60% HNO3 .…………….. 28.30% H3O .………………. 15.10% HNO3 ratio .………. 1.03 During the addition of the acid, the temperature is kept at 35-50 °C; but after the whole of the acid has been run in, the temperature is raise slowly to 65-70 °C and maintained at that period for 1 hr. The agitation is then stopped and the nitro naphthalene which floats on the surface is decanted with part of the spent acid and delivered to a separator, a “heel” of acid being left for the next nitration. After settling for 3 hr, the spent acid is removed and the crude nitro naphthalene is delivered to the washing and granulation kettle. Here it is made free for acid by repeated washings with boiling water and alkali. Any free naphthalene that may be present is removed by steam during the washing process. The crystallizing point must be between 52 and 52.5 °C.

The purification of the crude product is accomplished also by recrystallizing it from 10 percent of its weight of ligroin or solvent naphtha. The success of the purification depends upon certain details of manipulation, which include (1) use of a minimum of solvent and (2) constant agitation while re-crystallization take place in order to assure the formation of small crystals. The nitro naphthalene is dissolved in 10 percent of its weight of solvent naphtha and heated above the melting point of the crude, i.e., above 50 °C, until a homogeneous mixture is formed. The resulting solution is cooled to 25 °C with constant agitation, and the thick slurry that is formed is centrifuged. The α-nitro naphthalene obtained in this manner has a solidifying point above 54.4 °C. This is not yet pure, as the chemically pure material comes as glistening yellow crystals which melt at 61 °C.

PREPARATION OF NITROPARAFFINS The development of the preparation of nitroparaffins from laboratory scale through pilot plant to full scale operation covered a 20 year long effort by Commercial Solvents Corporation. A full scale plant with a capacity of more than 10,000,000 Ib per year went on stream in 1955. by a process of nitration of propane, the main production of nitroparaffins includes nitro methane, nitro ethane, 1-nitropropane and 2-nitropropane. The nitration is done in the vapor phase. A flow diagram illustration the process is shown in fig. There are five process sections in the nitroparaffins preparation. These involve (1) nitration, (2) products recovery (3) products purification (4) products separation and (5) reactants recovery. A report by Schecter and Kaplan states that conditions for the nitration of propane are 777 °F (410 °C) at pressure of 115-175 psi, initially the vapor phase was carried out in heated tubes through which a mixture of HNO3 vapor and hydrocarbon was ed. The present plant nitrator combines the two steps, using the heat of reaction to vaporize the nitric acid. Since, under perfectly balanced

Conditions, no heat would have to be added to, or removed from, the nitrator, it is called an adiabatic nitrator. In the form adopted, the nitric acid is introduced into a stream of heated hydrocarbon by a number of spray nozzles. Because of the high temperatures of 750-850 °F, short reaction times of 0.1-5.0 sec, and the corrosive properties of nitric acid, serious problems of design arose which have now been solved. The conditions of nitration can be varied widely, but these have been worked out to the optimum values of temperature, pressure, reaction time, ration of reactants, and the like. The proportion of the four nitro paraffins from propane is said by Bachman and Pollack to be about as follows:Nitro methane ……… 25% Nitro ethane …………10% 1-Nitro propane ……. 25% 2-Nitro propane ……. 40%

Nitrations in the vapor phase such as these are always accompanied by competing oxidative and decomposition reactions which may produce such organic materials as aldehydes, ketones, alcohols, carboxylic acids, olefins, nitrolefins, and polymers. Such simple compounds as CO2 and CO, NO, and H2O are also end products of the nitration reaction. The nitrator is operated to minimize production of nitrogen, and little excess nitric acid appears in the effluent stream. After leaving the nitrator, the product is cooled to condense the nitroparaffins and the pressure is reduced to atmospheric. The total effluent is then ed through an absorber, where it is scrubbed with a suitable solvent such as hydroxylamine hydrochloride which removes from the vapor phase the ketones, aldehydes, etc. This is done so that these will not be recycled to the nitrator with recovered propane. The gas from the absorber contain oxides of nitrogen and propane and are delivered to the reactants recovery process. The recycling of propane and recovered HNO3 leads to high yields of nitro paraffin based on HNO3. It is reported that over 90 moles of nitroparaffins may be obtained per 100 moles of HNO3 consumed. The liquid phase from the absorber is transferred to the top of a steam heated column called the stripper in which the crude nitro paraffins and water are stripped out of the solvent.

The regenerated solvent is recycled to the absorber. The stripped nitro paraffins along with water and the oxidation products are condensed and form a two layer mixture which is separated in a decanter. From the decanter the nitroparaffins layer is fed to the first rectification operation called the heads column.