Synthesis and Mass Spectrum Characterization of Lyrame Schiff Base for Synthetic Ingredients in Perfumes Industry

Introduction

The majority of personal-care such as cosmetic and perfumes contains fragrances in their ingridients.¹ Fragrance contains many components which have generated special properties, especially in odor. Ingredient of fragrance usually contains synthetic precursor or natural extract which is diluted in alcohol. Natural precursor provides unique odor,² but it has not been priority today due to dependence on weather condition which can disrupt the supply chain. Nowadays, synthetic precursor has been used to subtitute the natural source as a main ingredient.³

Quality of fragrance can be known from some properties, like odor, color, volatility, and other physical chemical stabilities.^4,5,6 Generally, a synthetic precursor is a Schiff Base like aurantiol,⁴ verdantiol, cyclantin, jasmea, and the most promising lyrame is added to escalate the quality of fragrances. Molecular weight of lyrame is bigger than other ingredients in fragrance, so lyrame Schiff base has good stabilty and less volatile. Its properties enhance the recilience of fragrance blend.

Aldehyde compound is reacted with amine trapping agent in condensation reaction to form Schiff base and water as a by-product. Water must be eliminated to prevent turbidity and two phases formed in product solution. Generally, eliminating water from product occurs under vacuum, instead using high temperature at atmospheric pressure to prevent Schiff bases product is not decomposing.³ The reaction of Schiff base synthesis as follows:

Figure 1: The formation reaction of Schiff base. Click here to View figure

 

Methyl anthranilate was often used as amine trapping agent in Schiff base’s synthesis. Methyl anthranilate generally gives Schiff bases that are yellow solid or viscous, yellow liquid. An excess methyl anthranilate was used to make Schiff base become more liquid. Methyl anthranilate is a primary amine which will react spontaneously with an alkyl aldehyde,⁷ terpened aldehyde,^7,8 or terpened-like aldehyde⁷ such as lyral. When methyl anthranilate reacts with lyral, Schiff base called lyrame is formed.

Gas chromatograpy and mass spectrometry (GC-MS) have been the most important techniques in the perfumes industry because perfume ingridient is quite complex, a polar, and (semi) volatile.^9,10,11 In this study, we aim to prepare lyrame Schiff Base using simple condensation reaction and to analyze spectral molecular ion fragment to ensure molecular structure lyrame Schiff base using GC-MS.

Figure 2: Mechanism of lyrame formation reaction. Click here to View figure

 

Lyrame Schiff base has a high molecular weight, meaning it has good physical and chemical stabilities, but poor solubility in water. In order to speed up the reaction, the synthesis was carried out at high temperature and stirred in hot plate. Furthermore, this process also prevented the solution turbid and formed two phases. Water would evaporate because the synthesis temperature was higher than boiling temperature of water. Stirring process during the synthesis would accelerate movement of water molecule, so would evaporate easily. The product solution was a bright yellow as shown in Fig 3.

Figure 3: (left) color of lyrame product solution; (right) lyrame product solution compared with lyrame standard solution. Click here to View figure

 

Color test was an important parameter for physical characterization in lyrame synthesis. Test was performed by trained panelist. The standard solution which used lyrame standard solution was made in PT Nilam Widuri. Time for synthesis of lyrame standard solution was 2 hours. Fig 3. shows that color in lyrame was light yellow. The lyrame product was brighter than standard, it was shown that color solution directly proportional with time of lyrame synthesis.

The concentration of methyl anthranilate was also a crucial factor to determine color the Schiff base. High concentration of methyl anthranilate gave a brighter color of solution and made product less viscous. Furthermore, another crucial factor determining the quality of product (brigthness of solution) was the degree of completion of reaction.

Figure 4: GC-MS chromatogram of lyrame’s synthesis. Click here to View figure

 

The lyrame product solution was analyzed by GC-MS to investigate lyrame molecular structure.^9,10 The result of GC-MS with percentage for each component was listed in Table 2. The reactant methyl anthranilate and lyral have peaks at 9.465 minutes, 12.513 minutes, and 12.571 minutes. It indicated that the lyrame formation was not completion. Lyral has two E-Z isomer configurating at its cyclic structure which shown in Fig 5.¹²

Figure 5: Skeletal formula of lyral isomers (a) Z-Lyral, (b) E-Lyral. Click here to View figure

 

Steric hindrance was an interaction that influenced the conformation in the organic molecules. Steric hindrance was a critical factor to determine the reactivity and stability in molecular structure.¹³ The molecule has less reactive in bulky molecules.¹⁴ Z-lyral has less steric hindrance than E-lyral, so Z-lyral would have more reactive than other isomer. It was proved with the unequal percentage of composition between isomers. Lyrame peak was shown at 22.350 minutes and 23.371 minutes. It exhibited that all lyral isomers could react with methyl anthranilate to form lyrame.

Table 2: Result of GC-MS analysis.

Retention time (minutes)	Compounds	Composition (%)	Molecular Formula
9.458	Methyl Anthranilate	28.38	C8H9NO2
12.513	Lyral	9.62	C13H22O2
12.571	Lyral	29.86	C13H22O2
22.350	Lyrame	27.67	C22H29O3
23.371	Lyrame	4.46	C22H29NO3

 

Figure 6: Mass spectrum of Lyrame from synthesis. Click here to View figure

 

Molecular structure of lyrame was investigated by using ion fragment from mass spectrometry. Fig 6 shows that mass spectral for lyrame product m/z 343 was similar with lyrame’s molecular mass and m/z 119.0 was the base peak. Mass spectra m/z 325 was originating from alpha cleavage releasing H₂O molecule. There were two possibilities of carbocation in m/z 325 tertiary and secondary positions. Double homolytic cleavages occurred in tertiary carbocation to produce C₃H₅⁺ which was shown as m/z 41. At secondary carbocation experiences the homolytic cleavage and C₄H₇⁺ were made. It was proved by peak of m/z 55 risen in fragmentation spectrum. Another route radical cleavage of secondary carbocation would release C₅H₉ radical and it was proved by peak of m/z 256 in the mass spectrum. Releasing ^–:CH₂ in next homolytic cleavage, made high peak of m/z 242 arise. Molecular ion C₁₅H₁₆NO₂⁺ experiences carbocation rearranged and followed by simultaneous heterolytic cleavage to release HCOOCH₃. The peak of m/z 77 was originating from C₆H₅⁺ which was rising after releasing C₇H₇N radical. The base peak of m/z 119 was originating from C₈H₆O₂⁺ which experienced homolytic cleavage to form C₇H₃O₂⁺ and released methyl radical. Pattern of lyrame’s mass fragmentation can be seen in Fig.6.

Figure 6a: Pattern of mass fragmentation of lyrame Schiff base. Click here to View figure

 

Conclusion

Lyrame Schiff base was succesfully synthesized by simple condensation method. The color of lyrame was directly proportional with time of synthesis. The degree of completion and concentration of methyl anthranilate also was crucial factor that affected the color of product. High concentration of methyl anthranilate made the product less viscous and the color of solution was brighter. Lyrame structural molecules has had been confirmed with GC-MS mass fragmentation pattern. There are two peaks of lyrame product in chromatogram due to lyral as precursor has two isomers that can be reacted with methyl anthranilate. Base peak in the lyrame fragment in m/z 119 is formed from homolytic cleavage C₈H₆O₂⁺ and the parental ions of lyrame fragment in m/z 343.

Acknowledgement

This research was funded by Politeknik AKA Bogor, Ministry of Industry of Indonesia and partially supported by from PT. Nilam Widuri for GC-MS measurement.

Conflict of Interest

The authors declare no conflicts of interest.

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