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Article

Analysis of a Probe of the Historical Dye Aldehyde Green Deposited in the Historical Dyestuff Collection of the Technical University Dresden

by
Susanne Machill
1,
Maximilian Voigtmann
1,
David Nescholta
1 and
Horst Hartmann
2,*
1
Bioanalytical Chemistry, Faculty of Chemistry and Food Chemistry, TU Dresden, 01062 Dresden, Germany
2
Historical Dyestuff Collection, Faculty of Chemistry and Food Chemistry, TU Dresden, 01062 Dresden, Germany
*
Author to whom correspondence should be addressed.
Colorants 2025, 4(2), 15; https://doi.org/10.3390/colorants4020015
Submission received: 13 March 2025 / Revised: 8 April 2025 / Accepted: 14 April 2025 / Published: 24 April 2025
(This article belongs to the Special Issue Feature Papers in Colorant Chemistry)
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Abstract

:
Aldehyde green, a dye first obtained by reacting fuchsine with acetaldehyde in 1862, consists of, according to analytical investigations carried out on a sample of this dye deposited in the Historical Dyestuff Collection of the Technical University Dresden and performed with liquid chromatography and high-resolution mass spectrometry, a mixture of various compounds in which the aniline groups of fuchsine are converted into quinaldine and dihydroquinaldine moieties. The dye owns its green color by two absorption bands in the visible range at 435 and 616 nm.

Graphical Abstract

1. Introduction

After F. F. Runge found in 1834, that a black dye, the so-called Aniline Black [1,2,3] could be produced quite easily from aniline (which was available in sufficient quantities in coal tar [4]), a few years later, a larger range of so-called aniline or tar dyes were produced, which very quickly gained great practical importance, especially as dyes in the textile industry [5]. These dyes included, among others, Aniline Violet or Mauveine [6,7], produced by W. Perkin in 1856; fuchsine [8], produced by E. Verguin and A. Hofmann in 1858; and the azo dyes [9] that were produced by various researchers, whose relatively simple synthesis was due to P. Grieß in 1863, who discovered that aromatic diazonium salts [10] were required for their production.
These, and a large number of other dyes made from aniline and its derivatives, exceeded the natural dyes previously used for textile dyeing in terms of color intensity and brilliance but were initially only available in shades ranging from yellow to red and violet to blue; therefore, green colors had to be generated by using a mixture of blue and yellow colorants. It was, therefore, a small sensation when the French chemist Usèbe produced the first green tar dye in 1862, named aldehyde green, by reacting the violet-coloring fuchsine with acetaldehyde in an acidic medium and with subsequent exposure to sulfur-containing reagents [11]. This green dye quickly became a fashion color in the English and French courts (Figure 1 and Figure S1) and was produced in Farbwerke Hoechst, Germany [12]. But, due to its low stability and a rather complicated manufacturing process, it was soon replaced by other green dyes, such as Iodine Green, made from fuchsine by J. Keisser in 1866 [13,14,15], and Malachite Green, discovered by O. Fischer in 1877 [16].
The relatively short period of using aldehyde green is probably one of the reasons why its exact chemical structure has not yet been elucidated, although, various researchers tried to do so in the last quarter of the 19th century. At this time, particularly by the studies led by Gattermann [17] and v. Miller [18], it was found that aldehyde green is a dye in which the three 4-amino-phenyl moieties originally present in Parafuchsine (A) have been converted into quinaldine or dihydroquinaldine rings. However, it remained unclear as to what the exact structure of the individual heterocyclic rings and the byproduct have, which occurs during the synthesis of aldehyde green, and is called Aldehyde Blue. In addition, it remained unclear as to what role the sulfur reagents played in the production of the dye and how the sulfur that was introduced into the dye molecules was bound.
For the production of aldehyde green, various process variants are used, which essentially differed in the time at which various sulfur-containing reagents, such as H2S, H2SO3, or Na2S2O3, were added to a mixture of fuchsine or Parafuchsine, an acetaldehyde derivative and a mineral acid. If these reagents are added during condensation between the fuchsine and appropriate aldehyde, sulfur-containing products should be formed, while sulfur-free products are obtained when these reagents are added after condensation, which is usually carried out at temperatures between 50 and 100 °C.
In their investigations, von Miller and Plöchl [18] also found that when the starting materials were heated in an acidic solution, the product obtained could be converted into a leucobase, which was assigned the structure G and, which, when reacted with hydrogen sulfide or sodium thiosulphate, converts into two different sulfur-containing products in their structures; however, only speculations were given. The authors postulated that when Parafuchsine (A) was reacted with acetaldehyde at RT, a compound of structure B was primarily formed, called Aldehyde Blue, which could be converted into compound C at a slightly higher temperature. This compound can be converted, depending on the production procedure, by H2S addition occurring at the two imino groups into two different compounds, for which structures with a disulfide bond between two side groups or the structures F or H were proposed (Scheme 1).
In connection with their attempts to elucidate the structure of aldehyde green, von Miller and Plöchl also found that the action of various reducing agents, such as tin in hydrochloric acid solution, produces a leuco compound, for which they proposed the structure G, and which is converted at the subsequent reoxidation using PbO2 in another blue dye, which is not identical to the Aldehyde Blue (B) proposed by Gattermann but is characterized by the presence of three dihydroquinaldine residues so that structure D was considered for it.
The ambiguities resulting from the aforementioned studies, as well as the inconsistencies resulting from today’s perspective regarding the structure of the quinaldine residue 2- or 4-methyl derivatives, resulting from the reaction of Parafuchsine or fuchsine with acetaldehyde and the structure of the sulfur-containing moieties, initiated us to commence a critical examination of the previously postulated structure of the historically important aldehyde green. For this purpose, an original sample of this dye, deposited in the Historical Dyestuff Collection of the Technical University Dresden, was used [19]. This sample bears the registration number 798, which is still given in the seventh edition of the Farbstofftabellen, edited by G. Schultz, from 1931 [20], but there is no indication of when and by whom this dye was produced and what definite elementary composition the fuchsine used for it had.
As is known, fuchsine is usually prepared by heating a mixture of the hydrochlorides of aniline, o-toluidine, and p-toluidine with an oxidizing agent, e.g., with nitrotoluene in the presence of metallic iron [21] or with As2O5 in a so-called arsenic smelt [20,22], so that one or two methyl groups can be present on its triphenylmethane skeleton.
Even though in the last decades there were several studies on the structure of historically important dyes (see, e.g., the refs [23,24,25,26,27,28,29,30,31,32,33,34,35,36,37]) published, appropriate studies on aldehyde green were not published to the best of our knowledge. This was the motive for us to elucidate the structure of a sample of the aldehyde green deposited in the Historical Dyestuff Collection of the TU Dresden with the devices and methods subsequently declared.

2. Methods

2.1. Elemental Analysis

The elemental composition of the original dye sample was determined with a LECO analyzer CHNS 932.

2.2. Thin-Layer Chromatography

This method was performed with TLC-Ready Plastic Sheets F1599 of Schleicher and Schüll on Silica gel using methanol/acetic acid (5:1) as eluent.

2.3. 1H NMR Measurements

The 1H NMR spectra were recorded in DMSO-d6 with a Bruker DRX 500P instrument at 500.13 MHz and are depicted in SI2.

2.4. UV/Vis Spectroscopy

The UV/Vis spectrum was measured in methanolic solution using the Varian Cary 50 spectrometer. The wavelength ranges from 350 to 800 nm, the signal average time is 0.1 s, the data interval is 1.00 nm, and the scan rate is 600.00 nm/min.

2.5. Liquid Chromatography-Mass Spectrometry (LC-MS)

The sample was dissolved in methanol and filtered with a 0.45 µm membrane syringe filter (NalgeneTM, Sartorius Stedim Biotech, Göttingen, Gemany). A total of 1 µL of the sample was injected into the instrument.
Chromatographic separations were conducted using an Agilent 1260 Infinity HPLC system; (Agilent Technologies, Waldbronn, Germany). An Agilent Poroshell 120 EC-C18 column with a length of 50 mm, a diameter of 4.6 mm, and a particle diameter of 2.7 µm equipped with a corresponding precolumn cartridge was used. In all experiments, a gradient of water containing formic acid (0.1 vol%), held for 2 min, with methanol, increased from 0 to 60 in 17 min, followed by another 10 min hold time, was applied. Water was purchased from Fisher Chemical, and methanol as well as formic acid were acquired from VWR Chemicals. The measuring time was 29 min, the flow rate was 0.5 mL/min, and the column temperature was 40 °C.
For detection, an Agilent 6538 UHD Accurate-Mass Q-TOF mass spectrometer with an ESI source was used; (Agilent Technologies, Waldbronn, Germany). All samples were measured in the positive ion mode with a capillary voltage of 3 kV, a fragmentor voltage of 60 V, and a skimmer voltage of 45 V. The nitrogen drying gas flow was 12 L min−1 at 300 °C, and the nebulizer worked with a pressure of 60 psig. Spectra were measured in the mass range of m/z 60 to m/z 1000. In the MS/MS experiments, the molecular ion of the component of interest was fragmented. The fragmentation energy was adapted to the component and ranged from 30 to 60 V. The measured spectra are depicted in Figures S3–S14.

3. Results and Discussion

The sample of aldehyde green used for the investigations represents a dark green powder, as shown in Figure 2(2). It is able to dye textile strips with a green color, as demonstrated in Figure 2(3).
The elemental analysis of the original sample of aldehyde green indicates that besides nitrogen in an amount of 6.1%, sulfur is present in an amount of 11.2%. In contrast, in a sample of the dye extracted with methanol, no sulfur is present. The 1H NMR spectra of both samples are depicted in Figure S1.
The UV/Vis spectrum of aldehyde green in a methanolic solution is shown in Figure 3. It exhibits two absorption bands at 435 and 616 nm, which are typically for a green colorant.
The TLC analysis indicated that the dye consists of several components and contains some traces of fuchsine (see Figure 2). A similar result was obtained from the NMR measurement. As can be seen from the 1H NMR spectra depicted in Figure S2 in the Supporting Information, a line-rich spectrum was obtained from which no conclusions could be derived about the presence of defined compounds.
Therefore, liquid chromatography was used to separate the mixture, and mass spectrometry was used for the structural investigation of the components. Figure 4 shows the LC chromatogram of aldehyde green as the Total Ion Current (TIC), which represents the sum of the intensities of ions over the whole measured mass range.
The chromatogram exhibited numerous signals, indicating the presence of many components in the sample, which means that aldehyde green is a complex mixture of different compounds. For evaluation, only peaks with higher intensities have been considered. Compounds occurring in higher amounts are marked in the chromatogram in Figure 4; for a detailed assignment, refer to Table 1. Their corresponding high-resolution mass spectra reveal the molecular weight and the elemental composition of the compound. As an example, the spectrum of one of the most abundant compounds at a retention time of 6.38 min (compound 12b) is shown in Figure 5.
The measured mass of the molecular ion at m/z 454.2262 confirms the elemental composition C32H28N3+ for this component. The deviation from the theoretical exact mass of 454.2278 is within the expected range of an experimental error (<0.002 mu). The most abundant peak in the spectrum at m/z 227.6165 results from a twofold charged ion, which is formed by the attachment of a proton onto the molecular ion. The deviation from the theoretical value of 227.6175 for C32H29N32+ again fits the experimental error.
In the chromatogram, further peaks with a mass distance of m/z 14 were detected. They are assigned to compounds 12a, 12c, and 12d (refer to Table 1). The Extracted Ion Current (EIC) of these ions is shown together with the TIC in Figure 6. These peaks indicate, justified by their exact masses, different methylation grades of the component mentioned above. These methyl groups may originate from the fuchsine used as an educt for the synthesis of aldehyde green.
The structure of these compounds may be proposed by fragmentation of their molecular ions using MS/MS experiments. As an example, the MS/MS spectrum of compound 12b with m/z 440.2134 (theoretical mass 440.2121) is shown in Figure 7. The two most intense signals in this spectrum are assigned to fragments of the molecule using their exact masses and known fragmentation rules. It is supposed that these ions are formed by the break of a bond at the central carbon atom of the triarylmethane center, followed by the addition of a proton. These ions, with a composition of C10H9N+ (m/z 143.0730) and C21H17N2+ (m/z 297.1391), may next lose a methyl radical, forming the ions with m/z 128.0501 and m/z 282.1156, respectively. Further ions with lower intensity in the MS/MS spectrum are formed by the loss of hydrogen or methyl radicals. Based on these results, a suggestion for the structure of this compound is given in Figure 7.
The structures of the methylated derivatives of this compound may also be confirmed by the fragmentation of their molecular ions. The MS/MS spectra of these compounds are shown in the Supporting Information in Figure S2. The fragmentation of the ion with m/z 454.2278 (compound 12b) shows additional signals with higher intensities at m/z 157.0889 and m/z 312.1618. This means that the corresponding ring systems must be methylated. In the MS/MS spectra of compounds with m/z 468.2439 (compound 12c) and m/z 482.2603 (compound 12d), the ring system is further methylated, as is evident from the signals at about m/z 326.178. No higher methylation of the ring systems seems to occur. The results exhibit that certain methyl groups are linked at the basic triarylmethane core of the dye, whereas their number and positions vary. However, the actual positions of the methyl groups are not estimable by mass spectrometry.
In this way, the molecular ions of the most abundant components in the chromatogram of aldehyde green are analyzed concerning their elemental composition, and the prevalent ones are fragmented to suggest their structures. The results are summarized in Table 1. Note that the intensity of the main chromatographic peak at about 4.1 min is not generated only from compound 18a but also from glycerol, which may occur as impurity. Parts of the chromatogram of aldehyde green containing EICs of molecular ions beside the TIC are shown in the Supporting Information in Figures S4–S9 for compounds 1, 5, 9, 10, 17, 18, and 21. These Figures support the data given in Table 1.
Additionally, the MS/MS spectra of the compounds derived from structure 9 are given in Figure S10. A proposed fragmentation mechanism for compound 9a is given in Figure S11. It proves the structure of this compound. The MS/MS spectra of compounds 9b, 9c, and 9d reveal the methylation of the ring systems again.
Figure S12 shows the MS/MS spectra of compounds of structure 17 with the proposed molecular ion structure and suggested fragment structures for compound 17a. The results prove the structure of this compound. The MS/MS spectra of compounds 17b and 17c reveal, again, the methylation of the ring systems.
The MS/MS spectrum of compound 18 is given in Figure S13 with an assignment of a few separated groups and with ion composition. All these data are based on the exact masses of fragments and support the structure of compound 18.
Further, a compound series with structure 21 is found in higher intensity. The MS/MS spectrum of compound 21b is given in Figure S14. Its structure is estimated from the fragmentation mechanism proposed in Figure S15.
Additionally, the identification of compound 1 as fuchsine is supported by the measurement of a fuchsine sample originating from the Historical Dyestuff Collection of the Technical University Dresden. Both consist of different isomers of methylated compounds with appropriate retention times.
Moreover, the evaluation of measured data by extracting the mass of molecular ions obtained from Scheme 2 shows some further components of aldehyde green occurring in traces. In this way, compounds with structures such as 2, 6, 8, 13, 14, 15, and 16 could be detected. Their presence supports the proposed reaction mechanism for the synthesis of aldehyde green given in Scheme 2.
All these data confirm the composition of the molecules given in Table 1 and allow us to develop a scheme for the reactions occurring during the formation of the aldehyde green sample. The result is given in Scheme 2.
However, it is not clear if all the isomers in these samples could be precisely detected because the chromatographic resolution of the device and its sensitivity are restricted. Note that the higher methylated compounds occur as different isomers, which is obvious from the peaks at different retention times in the chromatograms.
According to the mass spectroscopic data depicted at the measured peaks, the dye sample contains some components that result from the fuchsine used and/or from an incomplete reaction of this starting compound with acetaldehyde. Based on the historical studies mentioned above and the analytical investigations documented here, for the formation route and the structures of aldehyde green with its components, Scheme 2 is derived.
From the previously documented data on the structure and formation of aldehyde green with its components, the following conclusions can be drawn:
By treatment of fuchsine (1), which is used as a starting material, likely in the form of a mixture of Parafuchsine (1, R1,R2 = H) and some of its methyl derivatives, with acetaldehyde, the formation of crotonic aldehyde occurs, which reacts subsequently with the amino groups of the starting fuchsine derivatives in the course of a Michael addition [38] under formation of the adducts 2–4, which are transformed subsequently under elimination of water in course of a Skraub or Doebner–Miller heterocyclisation [39,40] into the corresponding dihydroquinolinium derivatives 5–7, respectively. These compounds were subsequently transformed into the heteroaromatic compounds 8–13 by dehydrogenation. In this way, triarylmethane derivatives with one, two, and three heterocyclic rings are formed from which the compounds 9, 12, and 17, respectively, seem the most favored ones, as detected in the mass spectroscopic measurements.
It is also worth mentioning that a compound with a molecular ion at m/z 160.0757, together with two methylated species, was detected in the dye sample. For this compound, the MS/MS spectrum is given in the Supporting Information in Figure S13. It reveals that structure 18 comes into consideration (Figure 8). At first glance, the presence of these compounds is surprising, but their existence in the original aldehyde green sample can be explained with the assumption that in the fuchsine educt used for the synthesis of this dye, anilinium (A0) as well as para-toluidinium (B4) and ortho-toluidinium salts (B2) were present (see Figure 2). Whereas the anilinium salt (A0) is able to react with acetaldehyde under the Skraub conditions, yielding, after oxidation, the quinolinium compound 18, which may occur with different methylations.
Additionally, a component with m/z 327.1492 and, therefore, a composition of C22H19N2O is detected together with some derivatives of smaller/higher methylation in the aldehyde green sample. This compound 21b results from the compounds 20 and 21 in a similar route. Compound 20 is an intermediate in the synthetic route for fuchsine, starting with a mixture of the mentioned salts of aniline, para- and ortho-toluidine, and is generated by an electrophilic attack of the iminium salt 19 at ortho-toluidine B2 and subsequent oxidation [41].
With respect to the color of aldehyde green, it can be seen from its absorption spectrum (refer to Figure 3) that it is characterized by two absorption maxima at 435 and 616 nm, which are typically for a green colorant [42]. Both absorption maxima result, owing to the structure of the dye as a triarylmethane derivative from two transitions perpendicularly oriented and originated by an electron transfer from a donor fragment onto an acceptor fragment [43]. Both fragments, namely an aniline or dihydroquinaldine moiety as a donor fragment, red, drawn in Scheme 2, and a quinoline moiety as an acceptor fragment, violet, drawn in Scheme 2, are present in compounds 9 and 12 and, hence, are responsible for the characteristic spectral behavior of aldehyde green. The expected color of the dye components 7, 10, 12, and 13 that result from the electronic structure of the side groups are indicated by the colored circles in this scheme.
It is worth mentioning that in the studied dye sample extracted by methanol, no sulfur-containing compound could be detected by LC-MS. However, from today’s perspective, with respect to the assumed formation of sulfur-containing compounds in the course of the synthesis of aldehyde green, it would also have been conceivable that a reaction of the Parafuchsine or one of its derivatives formed in the course of the dye synthesis with any sulfur-containing compound, such as sodium bisulfite, could be possible. Such a reaction would lead to adducts in which the used sulfur-containing reagent is bound to the central C-atom of the dye and can be removed from there in an acidic environment again. However, such reactions were not studied in detail earlier, but they were known later as the Schiff reaction and used as an indication reaction for aldehydes, which compete with the fuchsine for the bisulfite anion [44,45,46,47,48]. As a special aspect in the synthesis of aldehyde green, it seems that the possible formation of adducts between the dye and the sulfur-containing reagent generates non-ionic compounds, usually called pseudo bases [49], in which the aniline moieties become a higher basicity that raises their reactivity for a ring closure with the crotonaldehyde reagent.

4. Summary

The analytical studies of a sample of aldehyde green, deposited in the Historical Dyestuff Collection of the Technical University Dresden, were performed to show that this dye consists of a mixture of different compounds in which the aniline and toluidine moieties of the starting fuchsine are transferred into dihydroquinaldine and quinaldine moieties with electron-donating and electron-accepting properties, respectively, and that the simultaneous existence of both types of groups is responsible for the color of the dye. The analytical investigations of aldehyde green showed that no sulfur compounds were incorporated in the dye studied.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/colorants4020015/s1.

Author Contributions

Conceptualization, H.H. and S.M.; Validation S.M., M.V. and D.N.; Formal analysis S.M., M.V. and D.N.; Investigations S.M., M.V. and D.N.; Resources, H.H. and S.M.; Data curation, S.M.;Writing—original draft preparation, H.H. and S.M.; Writing—review and editing, H.H., S.M., M.V. and D.N.; Visualization, S.M., M.V. and D.N.; Supervision, H.H. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Acknowledgments

The authors thank Anett Rudolph for measuring the NMR spectra and Frank Drescher for their support with the LC-MS measurements.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Picture of Empress Eugenie surrounded by their ladies, painted by F. X. Winterthaler, see https://fashionhistory.fitnyc.edu/1855-winterhalter-empress-eugenie/.
Figure 1. Picture of Empress Eugenie surrounded by their ladies, painted by F. X. Winterthaler, see https://fashionhistory.fitnyc.edu/1855-winterhalter-empress-eugenie/.
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Scheme 1. Discussed structures of aldehyde green by different authors.
Scheme 1. Discussed structures of aldehyde green by different authors.
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Figure 2. Bottle of aldehyde green deposited in the Historical Dyestuff Collection of TU Dresden: (1) a sample of the dye, (2) a painted textile strip dyed with aldehyde green, (3) and TLC of fuchsine (a) and aldehyde green (b,c), (4).
Figure 2. Bottle of aldehyde green deposited in the Historical Dyestuff Collection of TU Dresden: (1) a sample of the dye, (2) a painted textile strip dyed with aldehyde green, (3) and TLC of fuchsine (a) and aldehyde green (b,c), (4).
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Figure 3. UV/Vis spectrum of aldehyde green in methanolic solution.
Figure 3. UV/Vis spectrum of aldehyde green in methanolic solution.
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Figure 4. The main part of the LC chromatogram of aldehyde green (Total Ion Current, TIC), where the identified components are marked. For assignment, refer to Table 1 and Scheme 2.
Figure 4. The main part of the LC chromatogram of aldehyde green (Total Ion Current, TIC), where the identified components are marked. For assignment, refer to Table 1 and Scheme 2.
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Figure 5. High-resolution mass spectrum of the chromatographic peak at about 6.4 min (compound 12b) in the chromatogram of aldehyde green with the insert showing the isotopic pattern of the two most intense signals.
Figure 5. High-resolution mass spectrum of the chromatographic peak at about 6.4 min (compound 12b) in the chromatogram of aldehyde green with the insert showing the isotopic pattern of the two most intense signals.
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Figure 6. Part of the LC chromatogram of aldehyde green; the black line represents the Total Ion Current (TIC), and the colored lines show the Extracted Ion Current (EIC) of ions with m/z 440.2121 (red), 454.2278 (blue), 468.2434 (green), and 482.2591 (orange), representing the most abundant compounds in aldehyde green.
Figure 6. Part of the LC chromatogram of aldehyde green; the black line represents the Total Ion Current (TIC), and the colored lines show the Extracted Ion Current (EIC) of ions with m/z 440.2121 (red), 454.2278 (blue), 468.2434 (green), and 482.2591 (orange), representing the most abundant compounds in aldehyde green.
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Figure 7. MS/MS spectrum of a compound with m/z 440.2134, measured with a fragmentation energy of 60 V, with proposed structures of the molecular ion and the two main fragments.
Figure 7. MS/MS spectrum of a compound with m/z 440.2134, measured with a fragmentation energy of 60 V, with proposed structures of the molecular ion and the two main fragments.
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Scheme 2. Formation routes and structures of aldehyde green; m/z for the appropriate components.
Scheme 2. Formation routes and structures of aldehyde green; m/z for the appropriate components.
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Figure 8. Assumed formation routes for the compounds 18a and 21b.
Figure 8. Assumed formation routes for the compounds 18a and 21b.
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Table 1. Main components detected in the chromatogram of aldehyde green, assigned by their exact masses, for compounds 9, 12, 17, and 18 additional by MS/MS spectra, and for compound 1 also by the retention times of a standard. For compound structures, refer to Scheme 2. Note that different retention times for one compound represent different isomers. As an area, the peak area of the corresponding EIC of the isomer with the highest intensity is given. The amount is divided into a major compound (+++, peak area > 108), main compound (++, peak area > 107), and minor compound (+, peak area >2.2 × 106 referred to 1% of main compound 12b). Other compound groups occurring in traces with peak areas <2.2 × 106 for the main compound are excluded.
Table 1. Main components detected in the chromatogram of aldehyde green, assigned by their exact masses, for compounds 9, 12, 17, and 18 additional by MS/MS spectra, and for compound 1 also by the retention times of a standard. For compound structures, refer to Scheme 2. Note that different retention times for one compound represent different isomers. As an area, the peak area of the corresponding EIC of the isomer with the highest intensity is given. The amount is divided into a major compound (+++, peak area > 108), main compound (++, peak area > 107), and minor compound (+, peak area >2.2 × 106 referred to 1% of main compound 12b). Other compound groups occurring in traces with peak areas <2.2 × 106 for the main compound are excluded.
CompoundCompositionExact MassMeasured MassRetention Time/minAreaAmount
1aC18H18N3+288.1495288.14889.331.3 × 106+
bC19H20N3+302.1652302.164010.776.1 × 106+
cC20H22N3+316.1808316.179710.87; 11.99; 12.909.9 × 106+
dC21H24N3+330.1965330.195011.99; 13.04; 13.50; 13.881.2 × 107++
eC22H26N3+344.2121344.211114.42; 14.77; 15.421.6 × 107++
fC23H28N3+358.2278358.226215.27; 15.90; 16.151.2 × 107++
5aC23H22N3+340.1808340.17933.678.2 × 106+
bC24H24N3+354.1965354.19523.872.3 × 107++
cC25H26N3+368.2121368.21084.23; 4.621.9 × 107++
dC26H28N3+382.2278382.22614.62; 5.10; 5.601.5 × 107++
9aC27H24N3+390.1965390.19533.892.8 × 107++
bC28H26N3+404.2121404.21044.35; 4.906.3 × 107++
cC29H28N3+418.2278418.22654.97; 6.08; 7.489.5 × 107++
dC30H30N3+432.2434432.24195.63; 7.06; 7.56; 9.04; 9.783.1 × 107++
10aC31H28N3+442.2278442.22605.826.3 × 106+
bC32H30N3+456.2434456.24208.081.1 × 107++
cC33H32N3+470.2591470.257510.09; 10.891.0 × 107++
dC34H34N3+484.2747484.272712.673.4 × 106+
12aC31H26N3+440.2121440.21074.376.5 × 107++
bC32H28N3+454.2278454.22626.382.2 × 108+++
cC33H30N3+468.2434468.241610.871.9 × 108+++
dC34H32N3+482.2591482.25729.79; 10.07; 17.364.8 × 107++
17aC31H26N3O+456.2070456.20543.971.6 × 107++
bC32H28N3O+470.2227470.22105.085.5 × 107++
cC33H30N3O+484.2383484.23687.665.5 × 107++
dC34H32N3O+498.2540498.252611.541.8 × 107++
18aC10H10NO+160.0757160.07484.121.2 × 108+++
bC11H12NO+174.0913174.09074.424.2 × 107++
cC12H14NO+188.1070188.10585.202.6 × 106+
21aC21H17N2O+313.1335313.132410.743.0 × 107++
bC22H19N2O+327.1492327.148717.58; 20.026.1 × 107++
cC23H21N2O+341.1648341.163721.592.5 × 107++
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Machill, S.; Voigtmann, M.; Nescholta, D.; Hartmann, H. Analysis of a Probe of the Historical Dye Aldehyde Green Deposited in the Historical Dyestuff Collection of the Technical University Dresden. Colorants 2025, 4, 15. https://doi.org/10.3390/colorants4020015

AMA Style

Machill S, Voigtmann M, Nescholta D, Hartmann H. Analysis of a Probe of the Historical Dye Aldehyde Green Deposited in the Historical Dyestuff Collection of the Technical University Dresden. Colorants. 2025; 4(2):15. https://doi.org/10.3390/colorants4020015

Chicago/Turabian Style

Machill, Susanne, Maximilian Voigtmann, David Nescholta, and Horst Hartmann. 2025. "Analysis of a Probe of the Historical Dye Aldehyde Green Deposited in the Historical Dyestuff Collection of the Technical University Dresden" Colorants 4, no. 2: 15. https://doi.org/10.3390/colorants4020015

APA Style

Machill, S., Voigtmann, M., Nescholta, D., & Hartmann, H. (2025). Analysis of a Probe of the Historical Dye Aldehyde Green Deposited in the Historical Dyestuff Collection of the Technical University Dresden. Colorants, 4(2), 15. https://doi.org/10.3390/colorants4020015

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