Breakdown of Мне нужно срочно поехать в офис за разрешением.
в
in / to (direction)
офис
office
мне
to me
нужно
it is necessary
Questions & Answers about Мне нужно срочно поехать в офис за разрешением.
Why do we use за разрешением instead of для разрешения to mean "for the permit"?
The preposition за followed by the Instrumental case specifically means going somewhere to fetch, retrieve, or pick up an object or person. If you used для with the Genitive case, it would mean "for the benefit or purpose of the permit," rather than expressing the physical action of going to get it.
What dictates the -ем ending on разрешением?
It takes the Instrumental case because it is the target of retrieval after the preposition за. Since разрешение (permit) is a neuter noun ending in -е, its Instrumental ending becomes -ем.
Why is the perfective verb поехать used here rather than an imperfective verb of motion?
The sentence describes a single, specific, completed trip that needs to happen right away. The perfective prefix по- applied to a verb of motion indicates setting off to a destination for a one-time result, fitting perfectly with the urgent need to retrieve the document.
Does the placement of срочно matter, and could I put it at the end of the sentence?
You could move it, but it would shift the emphasis. Russian typically places the most important new information at the end of a clause. Here, the main point of the trip is what you are going to get (за разрешением). Placing срочно at the very end would make the urgency itself the absolute main focus of your sentence.