• Author / Uploaded
• Winston Jake Gerolaga

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Names: Balo, Marielle

Date Performed: October 5, 2017

Gerolaga, Winston Jake

Date Submitted: October 20, 2017

EXPERIMENT 6 SYNTHESIS OF SULFANILIC ACID I.

Introduction

Sulfanilic acid (figure at the right), also known as 4-Aminobenzene-1-sulfonic acid in its preferred IUPAC name, is an off-white crystalline solid with a molecular formula C6H7NO3S. It has a molar mass of 173.19 g/mol and melts at 288 ˚C. It can be used to make dyes and various drugs and also in the quantitative analysis of nitrate and nitrite ions by diazonium coupling reaction with N-(1Naphthyl)ethylenediamine. It could be synthesized by the sulfonation of aniline. Further details about the mechanism of the reaction will be tackled in the discussion part of this laboratory report. The main goals for this experiment are: (a) synthesize sulfanilic acid by sulfonating aniline (as stated earlier) with concentrated sulfuric acid as a catalyst; (b) master techniques used in the synthesis of organic compounds; and (c) calculate for the percent yield of sulfanilic acid synthesized. II.

Methodology

To 9 mL aniline, 12 mL concentrated H2SO4 was added with careful swirling and cooling. The mixing was done in a 25-mL test tube. The mixture was then heated on a water bath for 2 to 3 hours until the sample yielded no oily aniline when added to dilute NaOH. The temperature was kept between 170 to 180 ˚C. It was then cooled to 50 ˚C in room temperature and then in an ice bath. The precipitate was collected by vacuum filtration using a Buchner funnel. The collected crude sample was then washed with cold water and decolorized by adding activated charcoal. It was recrystallized by adding enough hot water. The crystals were dried and weighed and was determined for the percent error. III.

Results and Discussion

Aromatic sulfonation is when benzene or substituted benzene reacts with SO3- in the presence of H2SO4 to yield sulfonated benzene. In this experiment, substituted benzene— aniline—is used as the reactant to produce sulfanilic acid. This reaction is also possible with the use concentrated H2SO4 with the presence of heat. In this case, H2SO4 was added to aniline and heated for about 2 hours in a sand bath to regulate the desired temperature maintaining the temperature to be within 170°C-180°C. Sulfonation reaction of aniline is shown as:

Aniline (C6H5NH2) undergoes sulfonation to form sulfanilic acid. It is benzene with an amino group attached to it. Consequently, benzene is a stable compound. However, reactivity of aniline increases because of the amino group present in it. This high reactivity is influenced by the amino group. The amino group, on the other hand, is an activating group or electron-donor, donating electrons to the ring to react to electrophiles. This high reactivity drives the reaction of sulfuric acid to aniline. Considering the structure of aniline; aniline is made up of two functional groups. These functional groups are composed of an acid and a base. The HSO3 constitutes the acid part of the sulfanilic acid. On the other hand, NH2 constitutes the basic part of the sulfanilic acid. These partial structures are derived from H2SO3 inorganic acid and NH3 inorganic base. Electrophilic substitution reaction refers to the reaction in which an electrophile substitutes another electrophile in an organic compound. Anilines undergo the usual electrophilic reactions such as halogenation, nitration and sulfonation. The functional group (-NH2) associated with aniline is electron donating group; it is very activating towards the electrophilic substitution reaction. Due to its various resonating structures, there is an excess of electron or negative charge over ortho- and para- positions of the benzene ring than the meta- position. Thus, anilines are o- and p- directive towards electrophilic substitution reaction. The amino group in aniline is an o,p director because it is a strongly activating substituent. Activating substituents follow the ortho and para positions when attacking the benzene ring (with the exception of halogens adjacently attached to the benzene ring since they are the only deactivating substituents that attack the benzene ring in an ortho, para manner) since they are far more resonance-stabilized by the aromatic system. In addition, they are also electrondonating substituents that donate these electrons through resonance. In electrophilic aromatic substitution, the resonance effect of amino group is more significant than its inductive effect. Aniline, this case, is the most activated benzene. It contains NH2 which is also the most activating group. Strongly activated rings like aniline can open up the ring to unwanted reactions. To avoid these unwanted reactions, the amino group undergoes reversible acetylation to make aniline moderately activated. The base, NaOH, is used to hydrolyse the acetyl group, and aniline with the wanted substituent is obtained. Table 1. Data for the masses Mass of the filter paper 1 (g) Mass of the crude sulfanilic acid (g) Mass of the filter paper 2 (g) Mass of crystalized sulfanilic acid + filter paper (g) Mass of crystalized sulfanilic acid (g)

0.5321 4.0934 0.5858 0.9822 0.3964

Mass of filter paper 3 (g) Mass of crystallized sulfanilic acid from waste + filter paper (g) Mass of crystallized sulfanilic acid from waste (g)

0.5387 1.2683 0.7296

The reaction between aniline and sulfuric acid to form the aniline hydrogen is exothermic. The heat of the exothermic reaction causes the temperature of the reaction mass to rise. To cause water to be split off and to promote the para-rearrangement of reaction at a slow but measurable rate, the minimum temperature must be about 165° C.-170° C. At this temperature, the aniline hydrogen sulfate is slowly converted, by an endothermic reaction, to sulfanilic acid. Sulfanilic acid, (in contrast to the aniline hydrogen sulfate salt) is stable and does not melt up to its decomposition temperature which is about 280° C. When the temperature is raised to the rearrangement temperature, the conversion starts. Sulfanilic acid is insoluble in molten aniline hydrogen sulfate. This result to the formation of molten mass becomes a pasty, sticky mass of a liquid phase and a dispersed solid phase. When water is present in the aniline hydrogen sulfate, the mixture forms a liquid or pasty mass at temperatures below 160° C. By maintaining the temperature of at least 160° C, the sample is converted into salicylic acid. During the water elimination the sample turns into a grayish or deep purplish product with indefinite composition. To purify this colored product and to remove the undesirable colored intermediates which affect the purity of the sample, a generous amount of activated carbon was mixed with the sample. It was then vacuum-filtered using Buchner funnel. The filtrate which contains the sulfanilic acid was placed in an ice bath to allow fast rate of recrystallization. After that, it is vacuum-filtered again and dried. At this instant, the dried sample is the purified solid sulfanilic acid. Compared with the grayish powderlike solid crude sample recovered, the recrystallized sample appears to be white crystals. Figure 1 shows all the data for the masses of the sample obtained all throughout this experiment. During the experiment; however, the filtrate for recrystallization was mixed with the filtrate of the other group. This leads to the recollection of the excess sulfanilic acid remaining from the filter paper. This is subjected again to filtration. Due to this error, two data for the mass of the crystallized sulfanilic acid was recorded. For the second trial, 0.3964g was obtained, and 0.7296g was crystallized from waste. This implies that a large amount of sulfanilic acid was discarded in the first trial. Table 2. Percent yield Trial 2 (%) From waste (%)

4.22 7.77

Table 3. Percent error Trial 2 (%) From waste (%)

95.78 92.23

As seen in table 2, greater amount of percent yield which is about 7.77% was obtained from waste than from trial 2 which is 4.22%. Overall, the total percent yield from this experiment is significantly low. The errors computed for this experiment are found to be 95.78% and 92.23% for trial 2 and from waste, respectively.

IV.

Conclusion

Sulfanilic acid was successfully synthesized from aniline. Two different masses of purified sulfanilic acid—0.3964 g for the second trial and 0.7296 g from the waste product— were obtained due to the human error committed. Overall, the original sample had 4.22% yield and the recrystallized sample from waste had a percent yield of 7.77% sulfanilic acid. For the next synthesis experiments it is recommended to familiarize the basic methods used for synthesis to avoid any errors that can affect the purity of the product or the product yield. V.

References

Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names 2013 (Blue Book). (2014). Cambridge: The Royal Society of Chemistry Hauptmann, S. (1985). Organische Chemie (2nd Ed.). Leipzig, Germany: VEB Deustcher Verlag für Grundstoffindustrie A Dictionary of Chemistry. (2000). Oxford University Press: Oxford Reference Online)s Jerffery, G. H., Bassett, J.H, (1989) Vogel’s Textbook of Quantitative of Chemical Ryan Capio, B.T., Lacson, D. & Estandarte, J. D. (2016). Synthesis of sulfanilic acid. Retrived October 15, 2017 from https://www.scribd.com/document/328097892/Preparation-of-SulfanilicAcid Lund, M. C., & Pass, M. C. (1989). U.S. Patent No. US4808342 A. Washington, DC: U.S. Patent and Trademark Office. Census data revisited. (2016, February 5). Electrophilic substitution of anilines. Retrived from byjus website, https://byjus.com/chemistry/electrophilic-substitution/