Aromatic acid chlorides dosage with N-acyl-aminoacids in aprotic solvents by a spectrophotometric method

Article abstract of DOI:10.1016/j.molliq.2010.04.001

The proposed method consists essentially in the treatment of an aromatic acid chloride solution with certain amounts of N-acyl-aminoacid as reagent. The mechanism of the colored chemical reaction is described here and the concentration of the aromatic acid chloride is determined on the basis of Bouguer-Lambert-Beer law. The results are discussed having in view the electrostatic interactions in the liquid solution in which the reaction takes place. The proposed method offers a high sensitivity, accuracy, easiness and quickness of the operations.

Full text of DOI:10.1016/j.molliq.2010.04.001

Journal of Molecular Liquids 154 (2010) 58–60
Contents lists available at ScienceDirect
Journal of Molecular Liquids
journal homepage: www.elsevier.com/locate/molliq
Aromatic acid chlorides dosage with N-acyl-aminoacids in aprotic solvents by a
spectrophotometric method
b
Sunel Valeriu a, Dorohoi Dana-Ortansa b, Moise Mihaela a, , Stroia Luminita
⁎
a
Faculty of Chemistry, “Al.I. Cuza” University, 11 Carol I BLdv., RO-700506, Iasi, Romania
b
Faculty of Physics, “Al.I. Cuza” University, 11 Carol I BLdv., RO-700506, Iasi, Romania
a r t i c l e i n f o
a b s t r a c t
Article history:
The proposed method consists essentially in the treatment of an aromatic acid chloride solution with certain
amounts of N-acyl-aminoacid as reagent. The mechanism of the colored chemical reaction is described here
and the concentration of the aromatic acid chloride is determined on the basis of Bouguer–Lambert–Beer
law. The results are discussed having in view the electrostatic interactions in the liquid solution in which the
reaction takes place. The proposed method offers a high sensitivity, accuracy, easiness and quickness of the
operations.
Received 18 December 2008
Received in revised form 12 March 2010
Accepted 2 April 2010
Available online 13 April 2010
Keywords:
© 2010 Elsevier B.V. All rights reserved.
Aromatic acid chlorides
N-acyl-aminoacids
Electronic absorption spectra
1. Introduction
oxazolinone-5 which is obtained by reaction between acid chlorides of
the one of the following reactants: N-(p-nitrobenzoyl)-L-phenylglicine
The methods applied for acid chlorides determination do not take
into consideration two functional components namely free chlorhid-
ric acid and R-COOH.
or N-(p-nitrobenzoyl)-L-phenylalanine [13].
2. Experimental part
In the majority of cases, R-COOH has an interference which is
either hidden [1], or determined as an acid chloride by titration with
Natrium acetate [2], or Natrium methoxide [3,4], or by precipitation
with AgNO3 [5,6]. The chlorides of the fatty acid with long chains are
treated with ammonium and then the halogenated acid is determined
by titration [7–11]. The quantitative analyses by titration, hydrolysis,
or precipitation are described in the articles mentioned above.
In order to avoid the difficulties which could appear because of the
methods described above when acid chlorides are dissolved, Yardimici
and Ozaltin [12] have elaborated a spectrophotometric method based
on the transformation of the acid chlorides into ferric-hydroxamates in
which the reaction medium becomes colored in red-purple.
Due to the hydroxamic acids which appear in alcoholic solution of
hydroxylamine (1 mol water/1 mL reactant) the resulted chlorhidric
acid can interact with water or with alcohol. This fact can induce
significant errors (≈10%).
The proposed method consists in the treatment of an acid chloride
in anhydric solvents by a given amount of N-acyl-aminoacid and
three-ethyl-amine, followed by a spectral analysis and by comparing
the results with the standard curves.
The reactants were prepared from 1.5 g of N-acyl-aminoacid and
2.08 g three-ethyl-amine in 25 mL dimethylformamide (DMF),
dichloromethane chloroform, acetone and dioxane.
Separately, the acid chloride solutions in anhydre solvents (chloro-
form and acetone) with a concentration of (0.5–4.0)10−3 mol/L were
prepared and then they were added to each N-acyl-aminoacid solution.
A red-violet coloration was obtained. The samples must be immediately
analyzed because their color persists only for 2–3 min. Then, the color
progressively disappears in a short interval of time [14–19].
The standard curves were obtained at fixed molar concentrations,
as it results from Fig. 1. Spectral measurements were made at Specord
UV VIS spectrophotometer with a data acquisition system.
In this paper a new method for the acid chlorides dosage is discussed.
It is more advantageous as regards the duration, simplicity and accuracy
of the results.
The proposed method is essentially based on the spectrophoto-
3. Results and discussions
metric determination of a colored anion of 2-(p-nitrophenyl)-4-R-Δ2-
Three acid chlorines from o-, m-, and p-nitro benzoic acids were
used in spectrophotometric measurements [20]. The graphs from
Fig. 1 indicate the applicability of Bouguer–Lambert–Beer law for the
spectral data.
⁎
Corresponding author.
E-mail address: moise_mihaela82@yahoo.com (M. Mihaela).
0167-7322/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.molliq.2010.04.001

S. Valeriu et al. / Journal of Molecular Liquids 154 (2010) 58–60
59
By measuring the absorbance in the maximum of the electronic
absorption band of chlorhidric acid having a known concentration,
between 0.3 and 0.7·10−3 mol/L, and comparing the results with
those obtained from the standard curves, the maxima of errors were
the following: ortho-nitro benzoic acid chloride — 0.11%; meta-
nitro benzoic acid chloride —
chloride — 0.09% (Table 1).
0.20%; para-nitro benzoic acid
The wavelength in the maximum of the electronic absorption band
of the chloral-anion was 522 nm for 2-(p-nitrophenyl)-4-phenyl-Δ2-
oxazolone-5 and 485 nm for 2-(p-nitrophenyl)-4-benzyl-Δ2-oxazo-
lone-5, respectively.
In basic medium, the reactions in the studied mixture lead to two
oxazolones and depend on the solvent nature (Fig. 2).
Let us consider that the apparition of the mixed anhydrides (AI, II
)
correspond to a SN2 mechanisms and it is favored by the electron
withdrawing effect of –NO2 substitute, on the carbon belonging to
carboxylic substitute from N-acyl-aminoacids I and II. On the other
hand the carboxylic group activation produced by the -p-nitrobenzoyl
rest, as well as the decrease in the strength of the hydrogen chemical
bond in the amyl substitute caused by the nitrophenyl rest could
explain the rapid cyclization of the mixed anhydrides AI, to the
II
oxazolones III and IV, the anions BI, II being more in rapport to the
anhydrides.
Concerning the apparition of the blue coloration, we think it is due
to the conjugated ion formed in the triethylamine presence in the
studied system, favored by the presence of three strong electron
withdrawing groups in the oxazolones' molecules (–C O; –C N; –NO2).
In these conditions, the hydrogen atom from α position is more
activated (Fig. 3).
4. Conclusions
A new spectrophotometric method for the analysis of the
aromatic acid chlorides was advanced by using two organic reagents:
N-(para-nitrobenzoyl)-L-phenylglycine and N-(para-nitrobenzoyl)-
L-phenylalanine.
The possibility of dosing the acid halides in the presence of HCl and
R-COOH in the same solvent where they have been obtained avoids
Fig. 1. Optical dependence of absorbance versus concentration for conpounds III and IV
(ortho, para, and meta).
Fig. 2. Reaction mechanism for obtaining oxazolones.

60
S. Valeriu et al. / Journal of Molecular Liquids 154 (2010) 58–60
Table 1
Results for fits of lines (1) from Fig. 1.
Substance
A
ΔA
B
ΔB(L/mol)
R
SD
N
P
III (o)
III (p)
III (m)
IV (o)
IV (p)
IV (m)
−0.0038 0.0023
0.0009 0.0003
0.0022 0.0003
0.0022 0.0035
0.2447 0.0009
0.1807 0.0012
0.99
0.99
0.99
0.99
1
0.0037
0.0046
0.0051
0.0056
6.29·10−17
0
9
9
9
9
9
9
0.0001
0.0001
0.0001
0.0001
0.0001
0.0001
0.12167 0.0013
0.1533 0.0015
−5.5·10−17 3.8·10−17
0.2 1.63·10−17
0
0
0.22
0
1
Fig. 3. Mechanism of the compartment of oxazolones III and IV in basic medium.
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their rather difficult separation with inherent decomposition and
losses by vaporization.
The anhydrous solvent also prevents from the hydrolysis reaction
which could generate significant errors.
A mechanism is advanced for the color reaction on which this
method is based.
This method shows several advantages over the other methods
known for the analysis of acid halides. Thus, it offers higher sensitivity,
accuracy, easiness and quickness of the operation.
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