Synthesis of 1-Phenylazo-2-naphthol PDF

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Synthesis of 1-Phenylazo-2-naphthol (Sudan-I) John Raymund B. Brusas | 2013-50015 Department of Mining, Metallurgical and Materials Engineering, College of Engineering University of the Philippines, Diliman, Quezon City 1101 Philippines Date Performed: February 14, 2014 Date Submitted: March 5, 2014...

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Synthesis of 1-Phenylazo-2-naphthol (Sudan-I) John Raymund B. Brusas | 2013-50015 Department of Mining, Metallurgical and Materials Engineering, College of Engineering University of the Philippines, Diliman, Quezon City 1101 Philippines Date Performed: February 14, 2014 Date Submitted: March 5, 2014

Abstract In this experiment, the synthesis of 1-Phenylazo-2-naphthol, commonly known as Sudan-I, was investigated. First was the production of the phenyldiazonium ion from 0.2 mL aniline and nitrous acid or the diazotization reaction. Next was the coupling reaction of the phenyldiazonium ion with 0.35g β-naphthol in 4.5 mL of 5% NaOH(aq). The crude product, Sudan-I, was recrystallized to eliminate impurities. At the end, 0.09g of recrystallized Sudan-I was acquired with a redorange color and a melting point range of 128-131°C. Also, the experiment had a percent yield of 16% while the purity of the synthesized Sudan-I was high or closely pure for its melting point was near to that of a pure Sudan-I which is 131132°C.

I. Introduction Amines are organic derivatives of ammonia in the same way that alcohols and ethers are organic derivatives of water. Like ammonia, amines contain a nitrogen atom with a lone pair of electrons [Figure 1], making amines both basic and nucleophilic. In fact, most of the chemistry of amines depends on the presence of this lone pair of electrons. They react with acids to form acid–base salts, and they react with electrophiles in many of the polar reactions (McMurry, 2008).

alkylamines because of their five resonance forms [Figure 2] (McMurry, 2008).

:NH2

+

NH2

:NH2

:Figure 2. Resonance structures of an arylamine making it more stable than alkylamine. +

Page 1

NH2

-: :

Alkylamines are prepared by SN2 reaction of ammonia or an amine with an alkyl halide while arylamines are prepared by nitration of an aromatic ring followed by reduction. Generally, arylamines are less basic than alkylamines because the nitrogen lone-pair electrons are delocalized by interaction with the aromatic ring π electron system and are less available for bonding to H+. In resonance terms, arylamines are stabilized relative to

+

NH2

I

Figure 1. General structure of an amine.

Amines react with alkyl halides by SN2 reaction and with acid chlorides by nucleophilic acyl substitution reactions. Amines also undergo E2 elimination to yield alkenes if they are first quaternized by treatment with

iodomethane and then heated with silver oxide, a process called the Hofmann elimination (McMurry, 2008). On the other hand, arylamines are converted by diazotization with nitrous acid into phenyldiazonium salts, ArN2+ X- [Figure 3]. The diazonio group can then be replaced by many other substituents in the Sandmeyer reaction to give a wide variety of substituted aromatic compounds. In addition to their reactivity toward substitution reactions, diazonium salts undergo coupling with phenols and arylamines [Figure 4] to give brightly colored azo dyes (McMurry, 2008).

NH2

+

N

N Cl-

NaNO2, HCl H2O, 0°C

Figure 3. Diazotization reaction, phenyldiazonium salt is formed from primary aromatic amines and nitrous acid. +

N

N

Y:

OH

+

-

Y:

N

N

Figure 4. Coupling reaction, the positively charged phenyldiazonium ion serves as the electrophile toward activated aromatic substrates, Y can be –OH (phenol) or –NR2 (arylamine). Many of the coupling products are used as acid-base indicators, food coloring compounds, biological staining Page 2

agents and as textile dyes (Organic Chemistry Lab Manual, 2008). Dyes are colored because they absorb light in the visible region. The functional group responsible for this are called chromophores, which mean “color bearers”. In azo dyes, -N=N- links two aromatic rings. This extended conjugation causes light to be absorbed in the visible region. In addition to chromophores, dyes have color augmenters or deepeners called auxochromes of the type –NHR, -NR2, -OH, and –OR (Organic Chemistry Lab Manual, 2008). In the art of dyeing, one must know both the structure of the dye and fiber to determine the method to be used. Some dyes are capable of direct dyeing with some fabric via chemical interaction called salt linkages. On the other hand, simple azo dyes do not directly bond well to cotton because of the absence of functional groups in the fiber responsible for the so-called chemical interaction. However, they are capable of dyeing cotton as a developed or ingrain dye. In this method, the dye is synthesized inside the fabric. Individually, the two components used to synthesize the dye will diffuse into the pores and spaces between the fibers in the fabric. After the individual components react inside the fibers, the dye is trapped within the fibers. The fully formed dye version of azo dyes will be too large to do this and could only bond to the surface of the fibers (Organic Chemistry Lab Manual, 2008). An example of an azo dye is 1-Phenyl-2-naphthol or Sudan-I. It is an orange-red dyestuff used in coloring waxes, oils, petrols and polishes. From the definition of an azo dye stated above, it is a product of a diazonium salt with a phenol or arylamine. By looking at the structure [Figure 5], its individual components are phenyldiazonium ion and β-naphthol. From here, we can synthesize Sudan-I using a phenyldiazonium salt and β-naphthol employing diazotization and coupling reactions. Also, we will apply the method of ingrain dyeing as one of the characteristics of azo dyes.

N=N OH

Figure 5. The structure of 1-Phenyl-2-naphthol (Sudan-I) is composed of phenyldiazonium salt and β -naphthol

II. Methodology

B. Preparation of β-naphthol solution

Synthesis of 1-Phenyl-2-naphthol

On the other hand, dissolve 0.35 g β-naphthol in 4.5 mL 5% NaOH(aq) in a beaker. Immerse in an ice bath and cool to 4°C. This will be solution B [Figure 6B] (Organic Chemistry Lab Manual, 2008).

Just for your safety: Wear a mask, rubber gloves and lab googles throughout the experiment. Sudan-I is carcinogenic and might enter your system. Materials and Apparatus aniline concentarted HCl NaNO2 crystals β-naphthol crystals 5% aq. NaOH 50 mL Erlenmeyer flask 50 mL beaker

ice bath thermometer rock salt cotton cloth 2x2 cm tweezers filter paper pipette

Ingrain Dyeing Place a fabric ( 2 x 2 cm) to be dyed in the cold βnaphthol solution, still immersed in an ice bath. Allow the fabric to soak for 2-3 minutes. Remove the fabric from the bath using tweezers and pat it dry between filter papers. Immerse the fabric in the phenyldiazonium chloride solution. After several minutes, remove from the solution and rinse well with running water. Note the color (Organic Chemistry Lab Manual, 2008). C. Synthesis of Sudan-I

B

A

C

Figure 6. Schematic diagram for the synthesis of Sudan-I.

A. Preparation of phenyldiazonium chloride solution In a 50 mL Erlenmeyer flask, combine 0.2 mL aniline, 0.35 mL water and 0.5 mL concentrated HCl. Immerse in an ice bath and cool to below 5˚C (you may use a thermometer to verify the temperature and add some rock salts to ensure the temperature is maintained). Then, add 1 mL ice-cold distilled water. Add 0.3 g NaNO2 crystal. Keep the temperature below 5˚C. This will be solution A [Figure 6A] (Organic Chemistry Lab Manual, 2008). Page 3

Now, add slowly while stirring the phenyldiazonium chloride solution (A) into the β-naphthol solution (B). This will be solution C [Figure 6C]. Allow the reaction to stand for 5 minutes at 4°C. Filter the product and wash it thoroughly with small portions of cold water (Organic Chemistry Lab Manual, 2008). Afterwards, proceed to recrystallization to purify the crude Sudan-I (See Recrystallization Process).

Recrystallization Process Recrystallization is one of the most important methods for the purification of solids. It involves the preparation of a saturated solution of the organic compound in an appropriate solvent at an elevated temperature and filtering this solution while hot. Insoluble impurities are removed during hot filtration. Upon cooling, the organic compound separates in the crystalline form leaving soluble impurities in solution (Organic Chemistry Lab Manual, 2008). The solvent plays a critical role in recrystallization. An ideal solvent should have the following properties: 

It should dissolve the solid readily at an elevated temperature and only sparingly at room temperature.





It should dissolve the desired solute but not the contaminant; or the desired component should recrystallize selectively from the solvent on cooling. It should not react chemically with the solute.



Solvent

Boiling Point (°C)

It should be sufficiently volatile to permit easy removal from the purified crystals (Organic Chemistry Lab Manual, 2008).

Table 1. Lists of solvents for recrsytallization with their melting points and which they are useful for.

Useful for

Common Co-Solvents

Water

100

Methanol Ethanol Acetone Ethyl acetate

65 78 56 77

Dichloromethane

40

Diethyl ether

35

Chloroform Toluene Benzene

62 111 80

Salts, amides, some carboxylic acids General use General use General use General use General use, low melting compounds General use, low melting compounds General use Aromatic compounds Aromatic compounds

Hexane

69

Hydrocarbons

Acetone, methanol, ethanol Water, diethyl ether, benzene Water, diethyl ether, benzene Hexane Ethanol, hexane Ethanol, hexane Methanol, ethanol, benzene Ethanol, hexane Ethanol, diethyl ether, ethyl acetate All solvents in this list except water and methanol Source: Organic Chemistry Laboratory Manual, 2008

cnx.org

Filtration Setup: fluted filter paper (2) stemless funnel iron stand iron ring beaker (receiving flask)

Figure 7. Filtration Setup. Use a fluted funnel paper to maximize the area for filtration and stemless funnel.

1. In a dry 25 mL Erlenmeyer flask, dissolve the collected impure Sudan-I in hot ethanol (ethanol is generally a good solvent for most organic compounds except for alcohols). Swirl/heat a bit until all the crystals are dissolve (you may add enough hot ethanol if there are still undissolved Page 4

crystals but note that if you add too much solvent you’ll get no crystals at the end). 2. Now that the pure crystals are dissolved, we can filter out the insoluble materials or the impurities. Filter the solution using a fluted filter paper [Figure 8] in a stemless funnel and a hot ethanol in a beaker at the receiving end (better if placed on a hot plate). Rinse the Erlenmeyer flask with a small amount of hot ethanol and filter again.

Figure 8. How to make a fluted filter paper.

quiz2.chem.arizona.edu

Materials and Apparatus crude Sudan-I ethanol hot plate ice bath pipette glass rod

Melting Point Determination Melting point is a physical property wherein an organic compound may be identified. Once the melting point was determined, one can examine its purity (Organic Chemistry Lab Manual, 2008). Material and Apparatus recrystallized Sudan-I crystals spatula watch glass capillary tubes (2) rubber bands

MP Determination Setup thermometer oil bath iron clamp iron stand hot plate rubber cork with hole

1. Pulverize the crystal using a spatula on a watch glass. Mound the pulverized sample and press the open end of the melting point capillary tube into the sample against the surface of the watch glass. Lightly tap the sealed end of the tube on the tabletop. Introduce more samples into the tube until the sample fills about 2-4 mm height. 2. Place 25 mL of oil in a dry 50 mL beaker. Insert a thermometer through a rubber cork, placing the rubber cork above the highest reading in the thermometer. Attach the melting point capillary tubes containing the sample to the thermometer by means of a thin strip of rubber bands. Be sure that the bulb of the thermometer as well as the capillary tubes are close enough to each other so that they Page 5

are both submerge in the oil bath and the rubber bands far enough that it will not be immerse in the oil otherwise it will melt with the hot oil. Clamp the thermometer by the cork and submerge in the oil bath.

Figure 9. Melting Point Determination setup. 

chemistry.mcmaster.ca

3. Afterwards, proceed to cooling down. Cool the solution slowly, from hot (boiling) to room temperature to 0°C (immerse in an ice bath). This is the recrystallization part. If the solution doesn’t start recrystallizing, scratch the inner sides of the beaker with a glass rod or (if you have) add a seed crystal. 4. Filter the solution to collect the pure crystals. Use a fluted filter paper and rinse the pure crystals with small amount of cold solvent (don’t redissolve the crystals). Let the crystals dry thoroughly overnight. Lastly, take its mass (Organic Chemistry Lab Manual, 2008). 5. To determine the purity of the recrystallized SudanI, proceed to melting point determination (See Melting Point Determination).

3. Make a preliminary test by heating the bath strongly and observing within 5°C the temperature at which the sample melts. After determining, cool down the oil. 4. Attach another capillary tube containing the same sample to the thermometer. Carefully determine the melting point by heating the bath slowly, about 3°C per minute, when the temperature approaches the melting point determined. As soon as the droplet of liquid forms in the tube (start of melting) until the last trace of solid has liquefied (end of melting), record the temperature reading. This will now be the melting point range of your compound (Organic Chemistry Lab Manual, 2008).

III. Results and Discussion As what stated in the introduction part, azo dyes like Sudan-I are synthesize through diazotization of an arylamine to a phenyldiazonium ion and afterwards the coupling reaction of the phenyldiazonium ion with an activated aromatic substrate. In the experiment, for the diazotization reaction part is the production of phenyldiazonium salt from aniline and nitrous acid (remember solution A). On the other hand, the coupling reaction is the formation of Sudan-I from the

phenyldiazonium ion and β-naphthol (that was solution C). Diazotization Reaction

N-nitrosoammonium ion then loses a proton to form an N-nitrosoamine, which, in turn, tautomerizes to a diazohydroxide in a reaction [Figure 13] that is similar to keto-enol tautomerization (Solomon, 2004).

+HA -HA

Figure 10. Schematic diagram for the diazotization reaction. Nitrous acid (HONO) is a weak, unstable acid that is why it is always prepared in situ. So, the role of NaNO2 and HCl is to produce the nitrous acid and nitrosyl cation (+NO) and a number of other species formed. For simplicity, organic chemists group all these species together and speak of the chemistry of one of them, nitrous acid, as a generalized precursor to nitrosyl cation [Figure 11] (Solomon, 2004).

H3O

+

H3O

Figure 13. Tautomerization of N-nitrosoamine to diazohydroxide . Then, in the presence of an acid, the diazohydroxide loses water to form the diazonium ion [Figure 14]. + +

+

-H2O nitrosyl cation

 Figure 11. Preparation of the nitrous acid using NaNO2 and decomposing to nitrosyl cation. After the formation of the nitrosyl cation, the diazotization reaction starts. There are three steps in this reaction: The nitrosyl cation (nucleophile) then reacts with the nitrogen of the aniline (having two lone pairs) to form an unstable N-nitrosoammonium ion [Figure 12] as an intermediate. N-nitrosoammonium ion then loses a proton to form an N-nitrosoamine (Solomon, 2004).

Figure 14. Phenydiazonium ion. Coupling Reaction Phenyldiazonium ions are weak electrohiles; they react with highly reactive compounds – with phenols and arylamines – to yield azo compounds (Solomon, 2004). Couplings between phenyldiazonium cation and phenols take place rapidly in slightly alkaline solution. Under these conditions an appreciable amount of the phenol is present as a phenoxide ion, ArO-, [Figure 15] and phenoxide ions are even more reactive towards electrophilic substitution than are phenols themselves (Solomon, 2004). OH

H3O

+

N-nitrosoamine

Figure 12. N-nitrosoamine from N-nitrosoammonium intermediate. Page 6

 Figure 15. Phenols couples slowly compare to phenoxide .

OH

With phenols and aniline derivatives, coupling takes place almost exclusively at the para position if it is open. If it’s not, coupling takes place at the ortho position (Solomon, 2004).

H2O

+ N N Cl

HCl

+ N N + Figure 18. Under temperature more than 5°C, phenyldiazonium ion reacts with nucleophilic substrates and producing aromatic compounds.

Figure 16. Coupling of the phenyldiazonium ion and β-naphthol resulting to 1-phenylazo-2-naphthol.

On the other hand, remember the coupling part, if the pH of the solution is too alkaline (pH > 10), however, the arenediazonium ion itself reacts with the hydroxide ion to form a relatively unreactive diazohydride or diazotate ion [Figure 19] (Solomon, 2004). OH

O-

Side Reaction Because the reaction is a bit unstable, it is not impossible for the reaction to give other side reactions. Most arenediazonium salts are unstable at temperature above 5-10°C, and many explode when dry. Once happened, the phenyldiazonium ion loses the nitrogen [Figure 17] as the leaving group and a carbocation is left. +

OH

HA

HA

Figure 19. Formation of diazohydroxide (middle) and diazotate ion (right) from a slightly basic medium. Data and Results

+

+ N N

Figure 17. Decomposition of phenyldiazonium ion under temperature greater than 5°C, producing N2 gas and an electrophilic ring. From here, H2O and HCl present in the reaction can react with the carbocation and produce phenol and chlorobenzene, [Figure 18] respectively. Page 7

-

-

OH

At the end, 0.09 g of Sudan-I was collected from 0.2 mL aniline and 0.3 g of β-naphthol. The melting point of the collected compound was determined to be between 128-131°C. The table below shows a tabulated data of the basic information from the reaction. Compound aniline β-naphthol Sudan-I (collected) Sudan-I (theoretical)

Volume 0.20 mL 0.24 cm3

Mass 7.75 g 0.30 g

Millimole 2.20 mmol 2.42 mmol

0.07 cm3

0.09 g

0.36 mmol

0.43 cm3

0.55 g

2.20 mmol

V. References

percent yield : 16%

[1] Mcmurry J., (2008). Organic Chemistry 7ed. Thomson Learning Inc. 919-959. [2] Univerisity of the Philippines, Diliman, Institute of Chemistry (2008). Organic Chemistry Laboratory Manual. 8-11, 86-89. [3] Solomons T.W., Fryhle C., (2004). Organic Chemistry 8ed. John Wiley & Sons, Inc. 963-972.

Table 2. Comparison of the volume, mass and no. of moles of the actual and theoretical yield. Properties

Sudan-I (collected)

Sudan-I (theoretical)

Color Melting point

red-orange 12...