INVESTIGATION OF THE THERMAL ANALYSIS OF NICKEL BENZENE-CONTAINING PHTHALOCYANINE PIGMENT

ABSTRACT

This article carefully details the findings of a study on the synthesis of a new pigment, copper calcium phthalocyanine, containing macroheterocyclic structures. This paper presents a comprehensive study on the creation of a new pigment - copper calcium phthalocyanine - incorporating macroheterocyclic frameworks. This article discusses the synthesis of a novel pigment, nickel phthalocyanine, characterized by the inclusion of macroheterocyclic compounds, and presents the corresponding research findings.This study investigates the thermal decomposition behavior of phthalic anhydride using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The experiments were carried out in an inert nitrogen atmosphere within the temperature range of 25–800 °C. The TGA results indicate a total mass loss of approximately 33.12%, leaving a stable residue of 66.88%. Significant decomposition steps were recorded at ~25 °C, 301 °C, 623 °C, and 684 °C. The DSC results revealed multiple exothermic peaks associated with the polymer breakdown process. These results highlight the potential of phthalic anhydride in controlled thermal applications and provide valuable insights into its thermal stability and decomposition mechanisms.

АННОТАЦИЯ

В данной статье подробно изложены результаты исследования по синтезу нового пигмента - медь-кальций фталоцианина, содержащего макрогетероциклические структуры. Работа представляет собой комплексное исследование получения нового пигмента - медь-кальций фталоцианина - с включением макрогетероциклических фрагментов. В статье рассматривается синтез нового пигмента - никель-фталоцианина, характеризующегося наличием макрогетероциклических соединений, и приводятся соответствующие результаты исследований. В данной работе также изучено термическое разложение фталевого ангидрида с использованием термогравиметрического анализа (ТГА) и дифференциальной сканирующей калориметрии (ДСК). Эксперименты проводились в инертной атмосфере азота в интервале температур 25–800 °С. Согласно результатам ТГА, общая потеря массы составила примерно 33,12%, при этом устойчивый остаток составил 66,88%. Существенные стадии разложения зафиксированы при ~25 °С, 301 °С, 623 °С и 684 °С. Результаты ДСК выявили несколько экзотермических пиков, связанных с процессом разрушения полимера. Полученные данные подчеркивают потенциал применения фталевого ангидрида в контролируемых термических процессах и предоставляют ценные сведения о его термической стабильности и механизмах разложения.

Keywords: Phthalic anhydride, nickel chloride, thermogravimetric analysis, thermal decomposition, differential scanning calorimetry, thermal stability.

Ключевые слова: Фталевый ангидрид, хлорид никеля, термогравиметрический анализ, термическое разложение, дифференциальная сканирующая калориметрия, термическая стабильность.

Introduction

Phthalocyanines (Pc) are macroheterocyclic compounds consisting of four isoindole rings interconnected through sp²-hybridized nitrogen atoms (Fig. 1).

Figure 1. Phthalocyanine compound

The founder of the chemistry of this class of compounds is considered to be Reginald Patrick Linstead, whose research group in 1934 purposefully synthesized phthalocyanine, its complexes with many metals, and carried out the first fundamental studies aimed at establishing their structure. It was Linstead who first introduced the term “phthalocyanine” into the literature [1]. In the future, this traditional name will be used, although according to IUPAC nomenclature the compound is designated as 5,28:14,19-diimino-7,12:26,21-dinitrilotetrabenzo-[c,h,m,r] [2,3,4] tetraazacyclo-icosine.

In the 1930s, detailed studies began on the practical application of phthalocyanines and their derivatives as dyes and pigments [5]. Since then, for more than 80 years, phthalocyanines have attracted close attention from researchers. During this time, many new substituted phthalocyanine ligands and their complexes with metals of various oxidation states have been synthesized and identified [6], which are being actively studied in many areas of organic, physical, coordination chemistry, and materials science.

Interest in the study of phthalocyanines is also due to their possible use in medicine for photodynamic therapy (PDT) and cancer diagnostics [7–8], as well as in technology for the development of gas sensors, solar cells, thin-film electronic devices, light-emitting diodes, photovoltaic devices, and so on [9].

More than 90% of the phthalocyanines produced worldwide (over 80,000 tons per year) are used as colorants—pigments and dyes [10]. Of this amount, approximately 40% are used in color printing inks, 30% in paints and coatings, 20% for coloring plastics, and 10% in other formulations [11]. Phthalocyanine derivatives account for approximately 25% of all commercially available synthetic organic pigments.

Materials and Methods

In the synthesis of the organic metal phthalocyanine pigment, 15 g of phthalic anhydride, 16 g of benzene, 13 g of nickel chloride, 60 g of urea, and an appropriate catalyst were placed into a heat-resistant 400 ml beaker. The components were carefully stirred at a lower temperature until complete dissolution was achieved. Subsequently, the reaction was carried out at temperatures ranging from 200 to 260 °C, forming a uniform and stable system. As a result of this carefully controlled reaction, a dark blue pigment was obtained. After the reaction, the mixture was cooled to room temperature and then placed in a vacuum oven for 120 minutes to dry. Following this, the pigment was cooled again and treated with concentrated sulfuric acid to remove any unreacted components. The sulfuric acid was added slowly along the inner walls of the beaker and stirred until a homogeneous mixture was formed. Then, boiling water was added to transfer the pigment into an acidic medium. The resulting acidic pigment suspension was washed several times with distilled water to neutralize the medium. After filtration, the pigment was dried in a drying oven at a controlled temperature of 60–80 °C.

The thermal stability of the pigment was studied using physicochemical analysis methods. The analysis was performed using a Netzsch Simultaneous Analyzer STA 409 PG (Germany) with aluminum crucibles. All measurements were carried out in an inert nitrogen atmosphere with a nitrogen flow rate of 50 ml/min. The temperature range was 25–370 °C with a heating rate of 5 K/min. The sample mass for each measurement was 5–10 mg. The measurement system was calibrated using a standard set of KNO₃, In, Bi, Sn, and Zn. A 10 mg sample of the investigated pigment was placed into a crucible (without a lid) made of alumina and platinum, resistant up to 1650 °C, with a diameter of 10 mm. The dynamic heating regime was conducted under atmospheric conditions.

Results and Discussion

The synthesized pigment demonstrated high thermal stability, excellent resistance to sunlight, and vivid color characteristics. These properties make it highly suitable for a wide range of practical applications. Importantly, the yield of the pigment at the end of the synthesis process was approximately 80%. During the analysis, the synthesized pigments were subjected to thermal analysis in the range of 20–500 °C. Furthermore, the endothermic and exothermic transitions of the pigments were confirmed. Fig.2 presents the results of the derivatogram analysis.

Figure 2. Derivatogram of the nickel benzene pigment NiC₆H₆Pc

The thermal properties of the NiC₆H₆Pc (nickel–benzene phthalocyanine) pigment were investigated using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The results demonstrated that as the temperature increased, the pigment underwent a multi-stage thermal decomposition process. The initial mass loss was observed at 25.11 °C, with a reduction of 1.864%, likely due to the release of adsorbed moisture or low-volatility surface components. The next significant stage of thermal degradation occurred at 300.92 °C, resulting in a 4.141% weight loss. This stage is attributed to the decomposition of unreacted organic residues or molecules that did not form stable complexes during the synthesis process. The most substantial degradation phase was recorded at 623.36 °C, where a 19.783% mass loss was observed. This phase corresponds to the breakdown of the primary phthalocyanine ring structure. Another stage of decomposition took place at 683.77 °C, where a 7.324% mass loss occurred, likely representing the final degradation of unstable organic fragments or pigment residues. Overall, the pigment sample exhibited a total weight loss of 33.112%, leaving a remaining residue of 66.882%, indicating the presence of a thermally stable portion of the pigment. This residue likely consists of nickel oxides (NiO) and stable carbonaceous components that withstand high temperatures. Furthermore, the DSC spectrum revealed several exothermic peaks, which are associated with the thermal decomposition of pigment components and possible phase transitions. Notably, the exothermic events occurring within the 200–700 °C range are thought to be related to structural transformations of the pigment and the breaking of chemical bonds.

Table 1.

Comparative thermal analysis of the nickel benzene phthalocyanine pigment obtained as a control

Received 45 mg of pigment NiC₆H₆Pc with a total mass

The NiC₆H₆Pc pigment undergoes its primary thermal degradation in the temperature range of 300 to 700 °C. The most significant weight losses were observed at 623.36 °C (19.78%) and 683.77 °C (7.32%), indicating that the decomposition of NiC₆H₆Pc occurs at relatively higher temperatures. This behavior confirms the comparatively high thermal stability of the pigment.

After thermal analysis, the NiC₆H₆Pc pigment retained 66.88% of its mass, suggesting the formation of thermally stable inorganic residues, likely consisting of nickel oxides (NiO) and possibly carbonaceous solid components.

Conclusion

The thermal analysis of NiC₆H₆Pc revealed the following key characteristics:

• A multi-stage decomposition process begins at relatively low temperatures (~25 °C).
• The major weight loss occurs at temperatures above 600 °C, indicating significant degradation of the molecular structure.
• After heating, approximately 67% of the residual mass remains, suggesting the formation of thermally stable carbonaceous structures.

These results indicate that the NiC₆H₆Pc pigment exhibits moderate thermal stability and can be safely used in chemical synthesis processes involving heating, provided that strict temperature control is maintained above 600 °C to prevent excessive decomposition.

Reference:

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