BAB II
TINJAUAN PUSTAKA
Diazonium salt is a precursor in the clutch and is often used for
synthesizing azo dyes. This dye is easy to stick on skin and clothing. Nitrogen at
the end of the diazonium cation is used as an electrophile in an electrophile on the
aromatic substitution reaction. Most of the product type brightly colored
diazonium coupling reaction known as Azo-dyes. Combinatorial synthesis is
needed to provide various types of compounds with various functions in a series
of reactions were carried out simultaneously (Mayo et al., 1994)
Azo dyes are found widely used as acid-base indicators. for example,
methyl orange and congo red well known and commonly used in the textile, food,
dyes and cosmetics industry (Atkens, 1990)
Azo compounds are usually very colorful because of the structure of azo -
N = N- read two rings into the conjugation. This allows the PI electron
delocalization and it allows the absorption of light (polarization) in the view.
Because of the intense color of azo compounds are those that can be synthesized
from a compound that is not common (Solomon, 1996)
Two typical indicators methyl orange and phenolphthalein. methyl orange
red preformance solution pH less than 3.1. In a solution with a pH above 4.4 is a
yellow substance. Indicator changes color as the chromophore system modified by
acid-base resonance. In acid solution, methyl orange as there is a resonance hybrid
of an azo structure terprotonkan, hybrid resonance is red (Fesserden....)
Reaksi methyl orange in the base (yellow)
Reaksi red in acid
Diazonium salts are very useful intermediates in the synthesis of the
aromatic compounds due to the diazonium group can be replaced by the anion of
the atoms or groups containing from -F,-Cl ...............and H. Almost diazonium
salt made of diazotized primary aromatic amines, arilamina primary nitro
compounds can be synthesized to produce direct experience nitration reaction
(Solomon, 1996)
Diazotized primary arilamina when reacted with nitric acid (generally
from NaNO2 in combination with sulfuric acid) the reaction occurred, whereby
the formation of a diazonium ion. reaction occurs under cold conditions. The
reaction is as follows (Zallinger, 1991):
Reaksi
Reaksi
Coupling reaction of aryl salt used to make the color of the substance
aniline and from aniline subatituted. In this reaction diazonium ion acts as an
electrophile diazonium ion resonance structures for the second show that nitrogen
has a partial positive charge. clutch products contain azo Group (-N = N-) and is
usually referred to as the azo compound. Many compounds of azo dyes substances
used as (Fessenden..........)
The reaction of the diazonium salt suitable couplings with aromatic
compounds as an example of electrophilic aromatic substitution reactions (as well
as aliphatic), an amine (Ar-NH2) is reacted with nitric acid (NaNO2 + HCL.... )
they can be converted to diazonium ArN2 cation (Mayo et al., 1994).
Azo compounds, color varies with the nature of the aryl group. Subtituen
pH also affects the solubility in water of azo dyes and how well they bind to
specific fabrics (Atkins....)
Crystallization is the process of forming dense phase a single component
of phase water namely multikomponen and can be done by means of cooling,
evaporation, or a combination of the two. The process of the formation of crystals
with three stages, namely:
1. The attainment of the condition of passing saturates
2. The formation of nucleus crystalline
3. The growth of the nucleus of crystals
Methyl orange is an azo compound shaped reddish yellow crystals, more
soluble in hot water and soluble in alcohol. Methyl orange is often used as an
indicator in acid-base titration. Methyl orange has a stretch pH 3.1 to 4.4 and a
pKa of 3.46, in a state of red and yellow in acid-base state. Methyl orange is used
to titrate the mineral acids and strong bases. Determine the alkalinity of the water
but can not be used for organic acid (Suirta, 2010)
Azo compounds can be either aliphatic and aromatic compounds.
Aromatic azo compounds are stable and have a glowing color. Aliphatic azo
compounds are more volatile. Azo compounds are used as dyes called ozodyes
(Christina et al., 2007)
