acid base extraction: naphthalene, 4-chloroaniline and benzoic acid

Acid-Base Extraction: Separation of an Organic Acid, Base and a Neural Compound

Introduction/Background Acid base extraction is a widely used commercial method in separating acids, bases and neutral compounds. This is concept is based on several physical properties of the compounds, such as boiling point, melting points and solubility. The different solubility properties of the protonated and non-protonated forms of these compounds depend on the functional groups present, such as carboxylic acids (acidic) and amines (basic). Since the compounds are being separated based on solubility and melting points, they must be in a solvent that is immiscible in nature; for example, ether and water. The organic acid compounds would be insoluble in water but is often soluble in ether. However, the basic solution added would deprotonate the organic acid and form an ionic salt. As a result, now this salt is soluble in the water rather than the ether. As Maurer and his colleagues states in their journal article that Proton transfer and acid-base neutralization reactions are among the most widespread and important transformations in chemistry and biology. (Maurer et al, 2010) This is why the technique is named as acid-base extraction because it is based on a series of acid-base neutralization reactions to extract the different solutions in the mixture; and then purify them by the processes of vacuum filtration. Therefore, the purpose of this lab is to extract a mixture of Benzoic acid, 4-chloroaniline and naphthalene, and characterize each compound by its melting point. Figure 1 from Solomon’s lab manual is shown below.
Experimental section

Table of Chemicals
Table 1
Chemicals used
Physical properties
Chemical properties
Diethyl ether
Molar mass = 74.12g; Melting point (MP)= -116 C; Boiling point (bop)= 34.6 C
A clear colorless liquid with an anesthetic odor
Clear liquid and highly flammable
Chemical formula= C4H10O
Benzoic acid

MP 121-125 C; Bop: 249 C

Molar mass= 122.12 g
White crystalline solid, slightly soluble in water
W

At high temperature Benzoic acid can react with oxidizing reagents. White crystals or powder.
Chemical formula=C7H6O2
Hydrochloric acid
MP= -114.9 C; Bop= -85.06 C
Molar mass=36.46 g Soluble in water; colorless gas with sharp, pungent odor
Reacts rapidly and exothermically with bases of all kinds. Acidic. Volatile and can be hazardous Chemical formula = HCl
Sodium Hydroxide
MP= 681 C; Bop= 145 C Soluble in water Molar mass=40 g
White solid, Basic. Reacts rapidly and exothermically with acids.
Naphthalene
White crystalline solid with distinctive odor of mothballs or coal tar. Molar mass=128.16 g. MP= 74 C. Bop 218
Chemical formula C10H8 Vigorous reactions, sometimes amounting to explosions, can result from the contact between strong oxidizing agents. Neutral in nature.
4-chloroaniline
MP= 67-70 C, Bop=232 C solubility in water=0.3g/100 ml
White, pale yellow solid. Stable. Combustible. Incompatible with strong oxidizing agents, acids, acid chlorides, acid anhydrides, nitrous acid. May be light sensitive.

Results
All compounds were massed and their melting ranges were estimated. The percent recoveries of each compound were calculated using the following formula.
Where 3 grams is the crude material used, and pure product recovered is the mass of all three compounds measured at the end of the experiment. Calculations are shown below:
For 4-Chloroaniline:
% recovery = 0.938 grams/3 grams x 100 = 31.2 %

For benzoic acid:
% recovery= 1.04 grams/3 grams x 100 = 34.7 %
For naphthalene:
Amount of product recovered= (mass of flask + naphthalene) – (mass of flask beaker)
Compound
Mass recovered (g)
Original melting point of compound (oC)
Melting range of the mass recovered (oC)
Percent recovery (%)
4- chloroaniline
0.938
68-71oC
61-65 oC
31.2 %
Benzoic acid
1.040
122 oC
104-108 oC
34.7 %
Naphthalene
4.052
80 oC
72-74 oC
135.06 % = 106.182 g – 102.13 g = 4.052 g
% recovery= 4.052 grams /3 grams =135.06 %
Table 2 below shows the percent recoveries of all three compounds as well as their masses and estimated melting point range compared to their original melting points.
Table 2:

Discussion The results generated from this experiment lead to a number of discussion topics. Acid base extractions are techniques involving chemical reactions that must be conducted with extreme caution. The percent recoveries for 4-chloroaniline and Benzoic acid are well under 50% which is an indication that most of product was not recovered. However it does not indicate how pure was the recovered product; that is indicated by the melting point. The low percent recoveries for the benzoic acid and 4-chloroaniline indicate possible loss of fluid or mass during transferring solutions from one flask to another and also during filtration. Some residual precipitate left over in the filter paper. It is almost impossible to transfer all the precipitate from one filter paper to another (during the drying process).
A recent study conducted by professors Tamada and King, of University of California states that the type of diluent and amine used in the experiment has a major effect of the extraction. (King et al, 1992).The percentage recovery for naphthalene was over a 100%, which is not practically possible. This indicates the product is not pure naphthalene. It is possible to have included some of the other compounds in the naphthalene while drawing it off from the separatory funnel. Another important reasoning to this is the possible error due to vacuum filtration. An inadequate vacuum filtration to could have lead to some water remaining in the naphthalene, which could have resulted in a much higher mass than expected; leading to a percent recovery of 135%.
Conclusion
After the analysis of the above results, it can be concluded that it is practically impossible to obtain a 100% purity in compounds extracted, unless the experiment is conducted on a micro-scale level. However, it does give successful results if performed with extreme care.

References
Thomas, V., Maurer, P., & Iftimie, R. (2010). On the Formation of Proton-Shared and Contact Ion Pair Forms during the Dissociation of Moderately Strong Acids: An Ab Initio Molecular Dynamics Investigation. The Journal of Physical Chemistry B, 114(24), 8147-8155.
Tamada, J. A., & King, C. J. (1990). Extraction of carboxylic acids with amine extractants. 2. Chemical interactions and interpretation of data. Industrial & engineering chemistry research, 29(7), 1327-1333.
Weldergima, S. (2012). Experimental Organic Chemistry. (p. 12). Mason, OH: Cengage learning.

References: Thomas, V., Maurer, P., & Iftimie, R. (2010). On the Formation of Proton-Shared and Contact Ion Pair Forms during the Dissociation of Moderately Strong Acids: An Ab Initio Molecular Dynamics Investigation. The Journal of Physical Chemistry B, 114(24), 8147-8155. Tamada, J. A., & King, C. J. (1990). Extraction of carboxylic acids with amine extractants. 2. Chemical interactions and interpretation of data. Industrial & engineering chemistry research, 29(7), 1327-1333. Weldergima, S. (2012). Experimental Organic Chemistry. (p. 12). Mason, OH: Cengage learning.