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Short Note

tert-Butyl N-Hydroxycarbamate (N-Boc-Hydroxylamine)

EaStCHEM School of Chemistry, University of St Andrews, North Haugh, St Andrews KY16 9ST, UK
*
Author to whom correspondence should be addressed.
Molbank 2023, 2023(3), M1728; https://doi.org/10.3390/M1728
Received: 31 August 2023 / Revised: 9 September 2023 / Accepted: 12 September 2023 / Published: 18 September 2023
(This article belongs to the Section Structure Determination)

Abstract

:
The X-ray structure of the title compound has been determined for the first time. This features ribbons formed by two parallel chains of molecules joined by C=O···H–N hydrogen bonding, which are then cross-linked by C=O···H–O hydrogen bonds. The structure is compared to those of closely related compounds.

1. Introduction

The simple compound tert-butyl N-hydroxycarbamate or N-tert-butoxycarbonylhydroxylamine 1 (Figure 1) was first reported in 1959 [1] and has proven to be useful in a number of recent applications, including the generation of t-Boc–N=O for use as a Diels Alder dienophile [2]. Such simple multifunctional compounds have the potential to form a wide range of interesting hydrogen bonding patterns in the solid state, and similar compounds such as the corresponding carbazate 2 [3], N-pivaloylhydroxylamine 3 [4] and tert-butyl carbamate 4 [5,6] have all been reported to show such patterns, as have a range of N-acylhydroxylamines such as 5 [7] and 69 [8]. We describe here the X-ray structure determination of compound 1.

2. Results

The compound was prepared using a method from the literature [9] involving the reaction of hydroxylamine hydrochloride, potassium carbonate and di-tert-butyl dicarbonate. It had physical and NMR data (see Supplementary Materials) in agreement with published values [9]. Crystals suitable for diffraction were obtained by recrystallisation from hexane. The resulting molecular structure (Figure 2) shows fairly conventional bond lengths and angles. The N-hydroxycarbamate functionality is quite accurately planar with a torsion angle O(1)–C(1)–N(1)–(O3) of +2.1(2)°. In fact, this is characteristic of the compounds of Figure 1 with none having a corresponding torsion angle above 12° (Table 1).
However, as expected, it is the pattern of interactions formed by hydrogen bonding that is more interesting. Each carbonyl oxygen is hydrogen bonded to the N–H and O–H of two separate adjacent molecules, resulting in a ribbon structure featuring a series of ten-membered rings (Figure 3, Table 2). The molecules are linked in two parallel chains by C=O···H–N bonding and these are then cross-linked by C=O···H–O hydrogen bonds, giving a graph set description of C(4)R23(10) [10].
Among the related compounds shown in Figure 1, the structure is most similar to that of N-pivaloylhydroxylamine 3 [4]. This also features a ribbon with each carbonyl oxygen hydrogen-bonded to the N–H and O–H of two separate molecules (Figure 4, Table 2). However, the important distinction is that, while 1 has the two chains of molecules aligned in parallel, in 3, they are antiparallel, and the structure can be viewed as a series of R22(10) dimers formed by C=O···H–O bonding, which are then joined in the chain by the C=O···H–N bonding, resulting in a first-order network of C(4)R22(10) and a second-order network of R24(10) [10].
Although it is not obvious from Figure 3, the ribbons of hydrogen-bonded molecules of 1 are not planar, but distinctly V-shaped. The angle between the mean planes defined by O(2), C(1), O(1), N(1) and O(3) of molecules on the two sides of the ribbon is 62.62(4)°. A view of the unit cell along the a-axis shows how the hydrogen-bonded chains of molecules are aligned in a zig-zag pattern (Figure 5).
By comparison, the remaining compounds identified in Figure 1 show an interesting variety of hydrogen bonding patterns. For tert-butyl carbazate 2, there are four independent molecules joined in a rectangular array by N···H–N (NH2) interactions, and these units are then joined in infinite chains by the C=O···H–N (NH) hydrogen bonding [3]. For tert-butyl carbamate 4, we have simple R22(8) dimers [5,6]. N-Propionylhydroxylamine 5 has three independent molecules and six separate hydrogen bonding interactions [7], and N-acetylhydroxylamine 6 has two independent molecules with five separate hydrogen bonding interactions [8], resulting, in each case, in highly complex three-dimensional networks. In contrast, the longer chain analogues N-hexanoyl-, N-decanoyl- and N-dodecanoylhydroxylamine 79 all form two-dimensional layers with a central region formed by only two hydrogen bonding interactions and an outer hydrophobic region accommodating the hydrocarbon chains [8].
In summary, we obtained the X-ray crystal structure of tert-butyl N-hydroxycarbamate for the first time and found the molecules to exist, when viewed along the b-axis, in cross-linked parallel chains with each carbonyl oxygen hydrogen bonded to both NH and OH of adjacent molecules. These then pack in a zig-zag pattern when viewed along the a-axis.

3. Experimental Section

NMR spectra were obtained for 1H at 500 MHz and for 13C at 125 MHz using an AV-III instrument (Bruker, Billerica, MA, USA). Spectra were run at 25 °C on solutions in CDCl3 with internal Me4Si as the reference. Chemical shifts are reported in ppm to high frequency of the reference. The melting point measurement was made on a Reichert hot-stage microscope (Reichert, Vienna, Austria).
Compound 1 was prepared using the literature method [9] as colourless crystals, mp 49–51 °C (ref. [9] 51 °C). δH (500 MHz) 1.475 (9H, s), 7.13 (1H, br s) and 7.24 (1H, br s); δC (125 MHz) 158.9 (C=O), 82.2 (C) and 28.2 (3CH3)—good agreement with ref. [9].
X-ray diffraction data for compound 1 were collected at 125 K using a Rigaku MM-007HF High Brilliance RA generator/confocal optics with XtaLAB P200 diffractometer (Cu Kα radiation (λ = 1.54187 Å), Tokyo, Japan). Data were collected and processed (including correction for Lorentz, polarisation and absorption) using CrysAlisPro [11]. The structure was solved by dual-space methods (SHELXT) [12] and refined by full-matrix least-squares against F2 (SHELXL-2019/3) [13]. Non-hydrogen atoms were refined anisotropically, and hydrogen atoms were refined using a riding model, except for the hydrogen atoms on N1 and O3, which were located from the difference Fourier map and refined isotropically subject to distance restraint. All calculations were performed using the Olex2 interface [14].
Crystal data for C5H11NO3, M = 133.15 g mol−1, colourless plate, crystal dimensions 0.21 × 0.12 × 0.02 mm, orthorhombic, space group Pbca (No. 61), a = 5.22500(10), b = 13.6564(2), c = 19.5261(2) Å, V = 1393.28(4) Å3, Z = 8, Dcalc = 1.270 g cm−3, T = 125 K, R1 = 0.0328, Rw2 = 0.0829 for 1392 reflections with I > 2σ(I) and 92 variables, Rint 0.0283, goodness of fit on F2 1.069. Data have been deposited at the Cambridge Crystallographic Data Centre as CCDC 2290327. The data can be obtained free of charge from the Cambridge Crystallographic Data Centre via http://www.ccdc.cam.ac.uk/getstructures.

Supplementary Materials

The following are available online, 1H and 13C NMR spectra, cif and check-cif files for 1.

Author Contributions

D.K.S. prepared the compound; D.B.C. and A.P.M. collected the X-ray data and solved the structure; R.A.A. designed the study, analysed the data and wrote the paper. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

The X-ray data are at the CCDC as stated in the paper.

Conflicts of Interest

The authors declare no conflict of interest.

References

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  5. CSD Entry: BIFPEL. Available online: https://www.ccdc.cam.ac.uk/structures/Search?Ccdcid=bifpel&DatabaseToSearch=Published (accessed on 30 August 2023).
  6. Bursavich, M.G.; Fronczek, F.R. tert-Butyl carbamate at 100K. Acta Crystallogr. Sect. C 1997, 53, IUC9700022. [Google Scholar] [CrossRef]
  7. Ferguson, G.; Glidewell, C. N-Propionylhydroxylamine forms a three-dimensional hydrogen-bonded framework structure. Acta Crystallogr. Sect. C 2001, 57, 452–454. [Google Scholar] [CrossRef] [PubMed]
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  10. Etter, M.C.; MacDonald, J.C.; Bernstein, J. Graph-Set Analysis of Hydrogen-Bond Patterns in Organic Crystals. Acta Crystallogr. Sect. B 1990, 46, 256–262. [Google Scholar] [CrossRef] [PubMed]
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  12. Sheldrick, G.M. SHELXT—Integrated space-group and crystal structure determination. Acta Crystallogr. Sect. A Found. Adv. 2015, 71, 3–8. [Google Scholar] [CrossRef] [PubMed]
  13. Sheldrick, G.M. Crystal structure refinement with SHELXL. Acta Crystallogr. Sect. C Struct. Chem. 2015, 71, 3–8. [Google Scholar] [CrossRef] [PubMed]
  14. Dolomanov, O.V.; Bourhis, L.J.; Gildea, R.J.; Howard, J.A.K.; Puschmann, H. OLEX2: A complete structure solution, refinement and analysis program. J. Appl. Crystallogr. 2009, 42, 339–341. [Google Scholar] [CrossRef]
Figure 1. Structure of compound 1 and similar crystallographically characterised compounds with CSD RefCodes.
Figure 1. Structure of compound 1 and similar crystallographically characterised compounds with CSD RefCodes.
Molbank 2023 m1728 g001
Figure 2. Molecular structure of 1 with anisotropic displacement ellipsoids drawn at 50% probability level and the numbering system used.
Figure 2. Molecular structure of 1 with anisotropic displacement ellipsoids drawn at 50% probability level and the numbering system used.
Molbank 2023 m1728 g002
Figure 3. Hydrogen bonding pattern in 1 viewed along the b-axis and schematic representation.
Figure 3. Hydrogen bonding pattern in 1 viewed along the b-axis and schematic representation.
Molbank 2023 m1728 g003
Figure 4. Hydrogen bonding pattern in 3 viewed along the b-axis and schematic representation.
Figure 4. Hydrogen bonding pattern in 3 viewed along the b-axis and schematic representation.
Molbank 2023 m1728 g004
Figure 5. V-shaped end view and unit cell of 1 viewed along the a-axis, showing the packing of hydrogen-bonded ribbons.
Figure 5. V-shaped end view and unit cell of 1 viewed along the a-axis, showing the packing of hydrogen-bonded ribbons.
Molbank 2023 m1728 g005
Table 1. Torsion angles in 1 and similar compounds.
Table 1. Torsion angles in 1 and similar compounds.
CompoundTorsion Angle(s) O=C–NH–OH a (°)Ref.
1+2.1(2)This work
2−9.5(3), +10.4(3), −4.5(3), +11.9(3)[3]
3−0.6(2)[4]
5−8.5(2), −6.5(2), −1.6(2)[7]
6−4.8(2), −8.2(2)[8]
7−9.1(5)[8]
8−8.5(6)[8]
9−8.7(5)[8]
a O=C–NH–NH2 for 2.
Table 2. Hydrogen bonding parameters for 1 (Å, °).
Table 2. Hydrogen bonding parameters for 1 (Å, °).
D—H···AD—HH···AD···AD—H···ARef.
1N(1)–H(1)···O(1)0.88(1)2.17(1)2.976(1)152(1)This work
1O(3)–H(3)···O(1)0.93(1)1.87(1)2.772(1)161(1)This work
3N(1)–H(1)···O(1)0.82(3)2.01(3)2.810(2)164(2)[4]
3O(2)–H(2)···O(1)0.91(2)1.74(2)2.647(2)171(2)[4]
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MDPI and ACS Style

Aitken, R.A.; Cordes, D.B.; McKay, A.P.; Sonecha, D.K. tert-Butyl N-Hydroxycarbamate (N-Boc-Hydroxylamine). Molbank 2023, 2023, M1728. https://doi.org/10.3390/M1728

AMA Style

Aitken RA, Cordes DB, McKay AP, Sonecha DK. tert-Butyl N-Hydroxycarbamate (N-Boc-Hydroxylamine). Molbank. 2023; 2023(3):M1728. https://doi.org/10.3390/M1728

Chicago/Turabian Style

Aitken, R. Alan, David B. Cordes, Aidan P. McKay, and Dheirya K. Sonecha. 2023. "tert-Butyl N-Hydroxycarbamate (N-Boc-Hydroxylamine)" Molbank 2023, no. 3: M1728. https://doi.org/10.3390/M1728

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